UC-NRLF 


B    3 


UNIVERSITY  STUDIES 

VOL.  XVII  JANUARY  1917  No.  i 


'A  STUDY  OF  THE  VEGETATION  OF  SOUTHEASTERN 
WASHINGTON  AND  ADJACENT  IDAHO  I 

A       £<\ 
BY  J.  E.  WEAVER 

TABLE  OF  CONTENTS 

PAGE 

Introduction   2 

Extent  and  position  of  area  4 

Physiographic  regions  and  geology   4 

Soils    6 

Topography  and  drainage   8 

General  plant-life  conditions    12 

General  veget'ational  distribution 15 

Outline  of  developmental  series  19 

Evaporation  and  soil  moisture  in  relation  to  succession  21 

Soil  temperature  in  relation  to  succession  37 

The  prairie-plains   formation    40 

Agropyron-Festuca  association   40 

Festuca  consociation  42 

Agropyron  consociation  59 

Rhizocarpon-Lecidea  associes    63 

Gyrophora-Parmelia  associes  65 

Grimmia-T ortula  associes  65 

Poa-Polygonum  associes  66 

The  desert  scrub  formation  71 

Artemisia- Atriplex  association    72 

Artemisia   consociation    72 

The  Pacific  Coast  forest  formation 73 

Thuja-Tsuga  association  74 

Symphoricarpos-Opulaster  associes  75 

Pinus-Pseudotsuga  associes  78 

Larix-Abies  associes  83 

Thuja  consociation   88 

I 


A  Study  of  the  Vegetation  of 


Adsere.    Alnus-Sali.v  associes  90 

Subsere.    Natural  reforestation  in  cut-over  areas  and  in  burns 91 

Hydrosere   100 

Chara-Potamogeton  associes    101 

Nymphaea-Potamogeton  associes   102 

Scirpus-Typha  associes    103 

Eleocharis-Carex   associes    104 

Wet  meadow  associes  105 

Flood-plain  forest  associes  107 

Ruderal  vegetation    109 

Conclusion    1 1 1 

INTRODUCTION 

No  one  at  all  botanically  inclined  can  travel  through  south- 
eastern Washington  without  being  impressed  with  the  marked 
changes  which  a  distance  of  only  a  few  miles  may  show  in  the 
vegetation.  Traveling  eastward  from  a  point  fifty  miles  west  of 
the  Idaho  state  line,  one  passes  from  a  region  of  scab-land  sage- 
brush through  one  of  rolling  hills  covered  with  bunch-grasses. 
Upon  steadily  ascending  the  great  Columbia  Plateau,  the  bunch- 
grasses  give  way  to  well  developed  prairies,  and  these  in  turn, 
near  the  Idaho  line,  to  forests  of  yellow  pine,  Douglas  fir,  white 
fir,  tamarack,  and  cedar.  Or  starting  from  Spokane  in  the  central 
part  of  eastern  Washington  and  traveling  southward,  one  soon 
leaves  the  pine  woodland  of  the  Spokane  gravels  and  passes  again 
through  the  rolling  prairies.  Projecting  above  the  surrounding 
sea  of  prairie-covered  basalt  are  islands  of  quartzite,  the  tops  of 
lofty  mountains  almost  buried  under  the  basalt.  These  may  be 
covered  with  grass  land  on  the  windward  side,  while  at  a  distance 
of  a  few  meters  over  the  crest  the  prairie  may  give  way  to  rather 
dense  forests.  Cut  through  the  layers  of  basalt,  in  a  mighty 
canyon,  1,600  feet  deep,  the  Snake  River  winds  its  way  through 
the  prairie  belt.  Upon  descending  into  the  canyon  one  finds  the 
bunch-grasses  and  sagebrush  vegetation  growing  in  a  climate 
markedly  different  from  that  of  the  plateau  above.  Far  south- 
ward from  the  canyon  of  the  Snake  River  rise  the  pine-covered 
foothills  of  the  Blue  Mountains. 

Such  is  a  brief  glance  at  the  wonderful  field  for  investigation 

2 


OK 

Southeastern  Washington  and  Adjacent  Idaho.  3 

offered  the  ecologist  in  southeastern  Washington.     It  is  a  field  in     ^Al  1 
which  many  stages  in  succession  are  offered  within  relatively  easy  i 

reach  of  a  base  station  and  one  in  which  the  vegetation  so  clearly  \A|  ^r 
reveals  adjustment  to  climatic  and  edaphic  conditions  that  one 
could  scarcely  wish  for  a  better  place  in  which  to  measure  the 
factors  of  the  habitat  and  the  vegetational  responses.  Moreover, 
in  this  great  inland  province,  practically  no  botanical  work  except 
of  a  taxonomic  character  has  been  done  (3,  9,  10,  n). 

Because  of  the  high  fertility  of  the  deep  basaltic  soils,  the 
prairie  region  has  largely  been  broken  up  for  the  growing  of 
wheat.  Indeed,  only  isolated  tracts  of  the  best  developed  prairies 
remain  intact,  while  hundreds  of  acres  of  the  drier  bunch-grass 
lands  have  been  broken  up  during  the  time  of  the  progress  of 
this  work.  It  seemed  unfortunate  that  a  record  of  the  rapidly 
disappearing  vegetation  of  this  interesting  region  had  not  been 
made.  Accordingly,  early  in  the  spring  of  1912,  reconnaissance 
work  was  begun,  with  Pullman,  Washington,  as  the  base  station. 

Ecological  work  was  pursued  vigorously  in  season  and  out 
(with  the  exception  of  the  summer  of  1912)  until  the  fall  of  1914. 

In  the  course  of  this  investigation  I  have  become  indebted  to 
several  persons  to  whom  I  wish  to  express  my  appreciation  for 
their  services.  I  am  pleased  to  express  my  appreciation  first  of 
all  to  Dr.  F.  E.  Clements,  of  the  University  of  Minnesota,  who 
visited  my  field  briefly  in  1914,  for  many  valuable  criticisms  and 
suggestions.  Dr.  Raymond  J.  Pool,  of  the  University  of  Ne- 
braska, has  read  the  first  draft  of  this  paper  and  I  am  grateful 
to  him  for  kindly  suggestions.  Thanks  are  due  to  Dr.  T.  C. 
Frye,  of  the  University  of  Washington,  for  the  identification  of  a 
number  of  mosses,  and  to  the  late  Dr.  H.  E.  Hasse  of  Santa  Mon- 
ica, California,  who  was  kind  enough  to  identify  all  of  my  lichens. 
Wilting  coefficient  determinations  of  soils  were  made  under  the 
direction  of  Dr.  L.  J.  Briggs,  of  the  United  States  Department 
of  Agriculture,  to  whom  I  wish  to  express  my  appreciation.  The 
chemical  and  physical  analyses  of  soils  were  made  by  the  depart- 
ments of  chemistry  and  soils  respectively,  of  the  Washington 
Agricultural  Experiment  Station  at  Pullman.  I  wish  further  to 
acknowledge  my  indebtedness  to  Mr.  Walter  L.  Muenscher  and] 


4  A  Study  of  the  Vegetation  of 

Mr.  Earle  Gibb,  my  one-time  students,  the  former  having  assisted 
me  in  the  field  during  the  entire  summer  of  1913,  and  the  latter 
during  1914.  Finally,  I  wish  to  express  my  appreciation  to  Dr. 
Harry  B.  Humphrey,  now  of  the  Bureau  of  Plant  Industry,  and 
formerly  my  colleague  in  the  Washington  State  College,  for  his 
kindly  interest  in  the  work  during  the  first  year  of  the  investiga- 
tion. 

EXTENT  AND  POSITION  OF  THE  AREA 

The  area  under  consideration  includes  approximately  4,000 
square  miles  of  territory  located  in  southeastern  Washington  and 
adjacent  Idaho.  On  the  south  it  extends  toward  the  foothills 
of  the  Blue  Mountains,  and  reaches  northward  to  the  vicinity  of 
Spokane.  Its  western  limit  is  about  50  miles  from  the  Idaho 
boundary,  while  in  Idaho  it  includes  a  strip  about  15  miles  in 
breadth.  This  area  lies  in  the  eastern  part  of  the  great  Colum- 
bia Plateau  and  extends  eastward  into  the  foothills  of  the  Bitter- 
root  Mountains.  The  47th  parallel  of  latitude  passes  through 
the  center  of  this  region,  while  it  is  bounded  approximately  on  the 
east  and  west  by  longitude  117°  and  118°  respectively.  Alti- 
tudinally,  it  ascends  from  about  1,175  feet  on  its  western  border 
to  a  height  of  4,000  feet  in  the  mountains.  The  lowest  point, 
about  520  feet,  is  reached  in  the  Snake  River  Valley,  while  Cedar 
Mountain,  near  the  Washington-Idaho  line,  reaches  a  height  of 
4,950  feet.  While  the  above  boundaries  limit  in  a  general  way 
the  investigations  recorded  in  this  paper,  without  doubt  the  vege- 
tation in  adjoining  regions  is  not  far  different  from  that  here 
described. 

The  peculiar  topography,  together  with  the  range  in  altitude, 
gives  this  area  three  clearly  defined  plant  formations,  ranging 
from  the  desert-scrub  formation,  through  the  prairie  formation 
to  the  Pacific  Coast  forest  formation.  A  brief  statement  of  the 
geology  and  topography  of  the  region  will  help  to  make  clear  the 
reasons  for  the  present  distribution  of  plant  communities. 

PHYSIOGRAPHIC  REGIONS  AND  GEOLOGY 

The  part  of  the  state  of  Washington  lying  east  of  the  Cascade 
Mountains  is  divided  naturally  into  three  great  physiographic 

4 


Southeastern  Washington  and  Adjacent  Idaho.  5 

provinces.  The  Okanogan  Highlands  occupy  the  northeastern 
part  of  the  state,  while  the  Blue  Mountains  cover  a  relatively 
small  area  in  the  southeastern  part.  The  remainder  and  larger 
part  of  the  area  makes  up  the  Columbia  Plateau. 

The  Okanogan  Highlands  consist  mainly  of  gently  rounded 
hills  rising  into  peaks  4,900  to  6,600  feet  high.  Geologically,  they 
are  similar  to  the  northern  part  of  the  Cascades  and  are  com- 
posed largely  of  granite.  They  form,  with  the  adjacent  moun- 
tains of  British  Columbia,  a  connecting  link  between  the  Cascades 
and  the  Rocky  Mountain  system  in  Idaho.  They  are  important 
in  connection  with  these  studies  mainly  for  the  ameliorating  effect 
they  exert  upon  the  climate,  and  for  the  role  they  have  played  in 
plant  distribution  in  the  foothills  of  the  Bitterroot  Mountains. 

The  portion  of  the  Blue  Mountains  occurring  in  Washington 
are  composed  wholly  of  basalt,  and  represent  a  great  uplift  of 
this  rock  surrounding  a  central  mass  of  granite  peaks.  In  Wash- 
ington they  reach  an  elevation  of  more  than  6,500  feet,  while 
in  Oregon  they  rise  about  3,300  feet  higher. 

The  Columbia  Plateau  is  thus  bounded  in  Washington  on  three 
sides  by  high  mountain  ranges,  while  in  Idaho,  on  the  east,  it 
merges  into  the  Bitterroot  Mountains..  The  plateau  forms  the 
greater  portion  of  eastern  Washington,  and  is  made  up  of  an 
immense  mass  of  basalt,  known  geologically  as  the  Columbia  River 
basalt.  This  basalt  is  the  result  of  a  series  of  lava  overflows 
which  involved  not  only  Washington,  but  also  large  areas  in 
Oregon  and  Idaho,  and  even  northern  California.  In  Washing- 
ton it  covered  all  of  the  region  south  of  the  Okanogan  Highlands 
and  extended  westward  from  the  Bitterroot  Mountains  to  the 
Cascades.  These  basaltic  lavas  were  extruded  in  a  highly  fluid 
condition  from  numerous  vents  thickly  strewn  over  the  floor  of 
the  region,  and  were  spread  over  the  surface  in  great  flows  (i, 
12,  13,  14).  The  apparently  flat  basaltic  plains  stand  out  in 
sharp  contrast  to  the  mountain  borders.  The  floor  upon  which 
the  lava  was  extruded  had  considerable  relief  and  was  not  greatly 
unlike  the  present  Okanogan  Highlands,  with  canyons,  gorges, 
and  mountain  peaks ;  the  whole  showing  a  state  of  vigorous  dis- 
section (14).  The  effect  of  the  basaltic  inundations  was  to  fill 


6  A  Study  of  the  Vegetation  of 

the  valleys,  and,  to  a  large  extent,  bury  the  old  topography.  An 
average  thickness  of  at  least  4,200  feet  has  been  estimated  for 
the  Columbia  basalt  in  Washington.  For  the  most  part,  the  Co- 
lumbia River  lava  completely  covered  all  of  the  older  rocks  over 
which  it  flowed.  Exceptions  to  this  appear  in  peaks  which  were 
too  high  to  be  overwhelmed,  such  as  Kamiak  Mountain  and  Step- 
toe  Butte  in  eastern  Washington.  Likewise,  old  divides  extend 
into  the  basaltic  fields  as  capes  or  promontories  against  which  the 
lava  came  to  rest.  These  older  rocks,  like  those  of  the  foothills 
of  the  Bitterroot  Mountains,  are  mainly  granites,  gneisses,  schists, 
and  quartzites.  Canyon  walls,  notably  those  of  Snake  River,  not 
only  reveal  the  older  rock,  but  also  expose  the  successive  lava 
flows  with  their  beds  of  dust  and  lake  deposits.  Snake  River 
has  cut  down  to  a  distance  of  over  1,600  feet  and  has  uncovered 
in  places  the  tops  of  buried  mountains.  Its  canyon  shows  at 
least  ten  overflows  of  the  lava.  Between  some  of  these  over- 
flows sufficient  time  elapsed  for  soil  to  form  and  forests  to  grow. 
The  evidences  of  the  latter  appear  either  as  charcoal  or  as  silici- 
fied  tree  trunks.  Geological  investigations  indicate  that  the  great 
outpourings  of  lava  were  antecedent  to  the  main  uplift  of  the 
Cascade  Mountains.  The  appearance  of  these  mountains  so  ef- 
fectually modified  the  climate  by  cutting  off  the  cool,  moist,  south- 
west winds  as  to  make  much  of  the  region  eastward  quite  too 
arid  for  forest  growth. 

SOILS 

The  basalt,  although  hard  and  resistant  to  forces  which  abrade 
it,  yields  with  comparative  rapidity  to  agencies  which  tend  to  dis- 
integration and  decay.  The  weathered  basalt  has  decomposed 
to  form  a  rich  residual  soil  which  mantles  the  surface  and  gives 
its  slopes  characteristically  soft,  rounded,  flowing  outlines.  It 
consists  of  a  friable,  dark-brown  silt  loam,  with  a  depth  ranging 
from  a  few  inches  to  several  feet.  The  subsoil  consists  of  a  light- 
brown  silt  loam.  It  is  heavier  and  more  compact  and  plastic 
than  the  surface  soil.  Both  soil  and  subsoil  are  extremely  re- 
tentive of  moisture.  They  form  a  mantle  usually  many  feet 
deep,  and  only  along  the  canyons  of  streams,  or  in  the  scab-rock 

6 


Southeastern  Washington  and  Adjacent  Idaho.  7 

in  the  western  part  of  the  area,  is  the  basalt  exposed.  Westward 
the  soil  becomes  lighter  in  color,  and  in  some  cases  is  impregnated 
with  alkali. 

Calkins  (i)  has  advanced  the  theory  that  the  soils  in  many 
parts  of  eastern  Washington  have  been  formed  by  wind  action 
and  are  not  of  a  residual  nature.  His  conclusion  is  based  upon 
the  facts  that  in  many  parts  of  southeastern  Washington  there  is 
an  absence  of  lamination  in  the  soil,  that  it  is  extremely  fine  in 
texture,  that  there  is  a  remarkably  sharp  definition  between  the 
soil  and  basalt,  and  that  comparative  chemical  analyses  indicate 
soils  not  of  the  character  naturally  to  be  expected  from  the  de- 
composition of  basalt  in  this  climatic  province.  He  believes  the 
principal  source  of  the  material  was  from  the  soft  sedimentary 
beds  in  the  southwestern  portion  of  the  Columbia  Plateau.  How- 
ever, the  fact  that  there  are  no  enclosed  and  undrained  basins,  as 
there  must  be  had  wind  been  the  only  agent  at  work,  leads  one 
to  conclude  that  water  erosion  has  also  been  an  important  factor 
in  forming  the  present  topography. 

By  the  action  of  water,  and  especially  the  prevailing  southwest 
wind,  the  plateau  has  been  moulded  into  rounded  hills  not  unlike 
sand  dunes.  The  soils  are  constantly  shifting  from  south  and 
southwest  to  north  and  northeast  slopes.  This  gives  better 
weathering  conditions  on  the  exposed  hillsides,  while  the  soils 
are  deepest  on  the  brows  of  the  slopes  where  there  is  the  most 
favorable  opportunity  for  the  accumulation  of  wind-blown  ma- 
terial. 

As  is  characteristic  of  dry  regions,  the  transition  from  soil  to 
subsoil  is  not  well  marked,  although  the  lighter-colored  subsoil 
appears  nearer  the  surface  on  exposed  than  on  sheltered  slopes. 
The  proportion  of  clay  is  greatest  towards  the  tops  of  the  hills. 
Humus  increases  as  one  goes  down  the  slopes  and  is  highest  in 
the  valleys,  where  it  forms  a  rich,  black  loam. 

In  contrast  to  the  silt  loam,  grit-free  soils  covering  the  basalt,  are 
the  sandy  loam  soils  formed  from  the  disintegration  of  quartzite, 
granite,  gneisses,  and  schists  of  the  buttes  and  mountains.  These 
vary  so  widely  in  mechanical  composition,  water  holding  capacity, 


8 


A  Study  of  the  Vegetation  of 


and  wilting  coefficient,  that  they  are  considered  in  connection 
with  the  plant  communities  which  they  support. 

TOPOGRAPHY  AND  DRAINAGE 

Viewed  from  the  top  of  a  bordering  mountain,  or,  better,  from 
the  summit  of  an  isolated  butte,  the  surrounding  plateau  looks 


FIG.  i.  Map  of  southeastern  Washington  and  adjacent  Idaho.  The  shaded 
areas  indicate  coniferous  woodland.  Most  of  the  outlying  timbered  areas  are 
characterized  by  yellow  pine.  West  of  the  dotted  line  and  in  the  canyon 
of  Snake  River  much  of  the  area  is  characterized  by  scab-land  covered 
with  sagebrush  or  bunch-grass. 

8 


Southeastern  Washington  and  Adjacent  Idaho.  9 

not  unlike  the  billowy  surface  of  the  ocean.  The  fine  silt  loam 
soil,  from  the  disintegrated  basalt,  has  been  moulded  by  the  ac- 
tion of  wind  and  water  into  a  dune-like  topography  (Fig.  38). 
Because  of  the  constant  shifting  of  the  soils  from  the  exposed 
south  and  southwest  to  the  leeward  slopes,  the  latter  are  much 
steeper.  These  hills  reach  a  height  of  100  to  360  feet.  Measure- 
ments of  a  large  number  of  slopes  near  the  base  station  gave  an 
average  gradient  of  12°  on  the  exposed  sides,  while  the  sheltered 
sides  were  from  5°  to  8°  steeper.  Indeed,  in  parts  of  the  region, 
many  of  the  hillsides  are  so  steep  that  they  can  not  be  brought 
under  cultivation.  The  intervening  valleys  are  usually  narrow, 
but  never  form  undrained  basins.  The  general  slope  of  the 
region  is  westward.  While  Thatuna  Hills,  a  low,  outlying  spur 
of  the  Bitterroot  Mountains,  culminate  in  Cedar  Mountain,  4,950 
feet  high,  the  eastern  edge  of  the  lava  sheet  reaches  an  altitude 
of  only  2,750  feet  (Fig.  i).  It  descends  at  the  rate  of  about  30 
feet  per  mile,  to  1,170  feet  on  the  western  border  of  the  region 
under  consideration. 

Two  main  rivers  with  their  tributaries  drain  the  region  except 
the  northeastern  part  which  is  drained  by  tributaries  of  Spokane 
River.  The  Palouse  River  has  its  headwater  tributaries  in  the 
mountains  of  Idaho,  and  after  passing  into  Washington  the  north 
and  south  forks  unite  at  Colfax.  In  the  western  part  of  the 
region  it  turns  southwestward  and  finally  enters  the  Snake  River. 
At  Colfax  the  river  has  cut  a  canyon  into  the  basalt  to  a  depth  of 
300  feet. 

In  general,  the  river  canyons,  whether  large  or  small,  are  char- 
acterized by  much  steeper  south  and  southwest  than  north  and 
northeast  banks.  This  is  due  in  part  to  greater  exposure  of  the 
north  and  northeast  sides  to  temperature  changes,  and  to  wind 
action  which  erodes  and  carries  away  the  soil  materials,  and  in 
part  to  the  constant  covering  of  the  sheltered  sides  by  wind- 
blown material.  These  processes  have  a  striking  effect  upon  the 
vegetational  cover.  Locally  the  exposed  canyon  walls  are  known 
as  rim-rock. 

Snake  River  is  joined  by  the  Clearwater  as  it  enters  Washing- 
ton. Tributaries  of  the  latter  drain  the  extreme  eastern  part  of 

9 


io  A  Study  of  the  Vegetation  of 

the  region.  Snake  River  flows  westward  through  the  region  in  a 
canyon  which  is  simply  an  immense  gorge  a  mile  and  a  half  to 
two  miles  wide  hewn  in  the  basalt.  Although  'the  canyon  is 
over  i, 600  feet  deep,  the  river  has  not  yet,  except  in  a  very  few 
places,  cut  to  the  bottom  of  the  basalt,  for  its  present  bed  is  still 
like  its  bluffs.  The  soil  of  these  bluffs,  as  is  characteristic  of 
similarly  exposed  situations  in  the  region,  presents  various  stages 
of  decomposition  from  the  coarse  talus  at  the  foot  of  the  cliff  to 
well  formed  soil.  The  canyon  at  its  bottom  is  scarcely  wider 
than  the  river,  except  at  the  bends,  where  bars  of  moderate  area 
have  been  formed.  The  soil  of  the  bars  is  partially  river-sand 
of  granitic  origin  and  partially  wash  from  the  bluffs. 

Except  for  the  Clearwater,  no  large  streams  enter  Snake  River 
in  this  region.  Numerous  small  laterals  have  worked  their  way 
back  into  the  basalt,  and  it  is  along  these  that  the  main  canyon 
may  be  entered,  especially  from  the  south. 

In  general,  the  topography  is  young.  The  streams  have  not 
advanced  far  in  their  task  of  cutting  away  the  rocks  from  the 
plateau  and  of  reducing  the  land  to  base  level.  Especially  south 
of  Snake  River,  in  Garfield  County,  where  the  surface  is  less  roll- 
ing, one  is  impressed  with  the  view  of  a  land  with  a  broad  plateau 
surface  and  an  infantile  drainage.  Here  the  spaces  between  the 
streams  are  flat-topped. 

In  the  northwestern  part  of  the  area  occur  numerous  small 
lakes,  of  which  Rock  Lake,  about  0.5  mile  wide  and  7  miles  long, 
is  the  largest.  It  is  really  a  great  crack  in  the  basalt,  with  rocky 
canyon  walls  and  basalt  bottom.  It  connects  northward  with 
Little  Rock  Lake  and  is  drained  into  the  Palouse  River  by  Rock 
Creek. 

About  these  lakes,  as  well  as  along  the  canyons  of  the  streams, 
the  weathering  of  the  edge  of  the  basaltic  sheets  has  caused  them 
to  recede  unequally  and  to  form  steps  or  terraces  in  the  faces  of 
the  precipices.  Where  the  walls  are  steepest,  they  present  a 
series  of  narrow  steps  covered  with  talus  and  soils  in  all  stages  of 
formation,  separating  vertical  masses  of  bare  and  frequently 
columnar  rock  30  or  more  feet  in  height  (Fig.  45). 

In  the  drier  western  part  of  the  region,  where  the  disintegra- 

10 


Southeastern  Washington  and  Adjacent  Idaho.  n 

tion  of  the  basalt  is  correspondingly  of  a  smaller  degree,  the  rock 
often  crops  out  upon  the  surface.  Such  rocky  lands  are  known 
locally  as  scab-lands.  They  often  occupy  what  appear  to  be  for- 
mer river  valleys,  although  they  are  now  dry  or  contain  only  small 
streams  or  small  groups  of  lakes.  These  valleys  may  be  of  con- 
siderable extent;  the  local  names,  "Eight-mile  Flat,"  "Twelve- 
mile  Flat,"  etc.,  indicate  their  size. 

Owing  to  the  porous  nature  of  the  basalt,  as  well  as  to  sheets 
of  clay,  sand,  and  gravel  interspersed  between  the  successive 
layers,  springs  are  numerous  throughout  the  region.  Oftentimes, 
wells  dug  merely  into  the  soil  afford  a  good  supply  of  water, 
although  they  are  usually  drilled  into  the  basalt  (8).  In  other 
cases,  as  at  Pullman,  an  abundant  supply  of  fine  artesian  water 
is  obtained  from  beds  of  sand  and  gravel  between  the  layers  of 
basalt. 

Standing  above  the  surrounding  plateau  are  numerous  isolated 
buttes  and  several  ranges  of  low  mountains.  These  are  the  tops 
of  lofty  mountains  not  overwhelmed  by  the  flood  of  basalt. 
Among  the  former,  Steptoe  Butte,  a  perfectly  conical  peak  with 
an  altitude  of  3,613  feet,  is  a  landmark  to  be  seen  for  miles. 
Likewise,  Kamiak  Mountain,  running  from  east  to  west  for  a 
distance  of  over  two  miles,  and  reaching  an  altitude  somewhat 
greater  than  Steptoe  Butte,  is  equally  prominent.  In  some  cases, 
only  a  few  acres  of  the  tops  of  buried  mountains  show  them- 
selves above  the  basalt.  Such  a  butte  may  be  seen  just  west  of 
Bald  Butte,  the  culmination  of  a  ridge  of  quartzite  running  out 
southwestward  from  Thatuna  Hills.  Tekoa  Mountains,  near 
Tekoa,  Washington,  are  a  low,  outlying  ridge  of  the  Bitterroot 
system.  They  reach  a  height  of  4,000  feet.  Gold  Hill,  not  far 
from  Potlatch,  Idaho,  is  the  highest  point  (about  4,500  feet)  of 
another  group,  while  Cedar  Mountain  (4,950  feet),  northwest  of 
the  Clearwater  River  in  Idaho,  is  the  highest  point  of  a  consider- 
able range  known  as  Thatuna  Hills.  These  buttes  and  mountains 
are  very  old  geologically  as  compared  with  the  basalt,  and  are 
well  eroded  and  mostly  forest-covered.  Southeastward  their 
streams  empty  into  the  Clearwater  River.  Elsewhere  they  are 

1 1 


12  A  Study  of  the  Vegetation  of 

drained  by  the  Palouse  River  and  in  the  extreme  northeast  by 
tributaries  of  Spokane  River  (Fig.  i). 

GENERAL  PLANT-LIFE  CONDITIONS 

Hemmed  in  on  all  sides  by  mountains  the  region  under  consid- 
eration has  a  climate  much  warmer  and  much  drier  than  one 
would  expect  at  this  altitude  and  latitude.  The  Okanogan  High- 
lands on  the  north  shelter  it  from  cold  winter  winds,  while  on  the 
east  and  south  it  is  protected  by  the  Bitterroot  Mountain  system 
and  the  Blue  Mountains,  respectively.  The  Cascades  on  the 
west  intercept  the  rain-bearing  westerly  winds  from  the  Pacific 
Ocean.  Even  where  the  prevailing  southwest  wind  cutting 
through  the  mountain  gap  of  the  Columbia  River  and  rising  over 
the  high  plateau  drops  much  of  its  moisture  near  the  high  eastern 
border,  the  annual  precipitation  is  only  21.6  inches.  Westward 
it  decreases  steadily  with  decreased  elevation,  giving  an  annual 
precipitation  of  only  10-13  inches  near  the  western  boundary  of 
the  region. 

In  this  semi-arid  region  where  evaporation  rates  are  very  high, 
a  knowledge  of  the  distribution  of  rainfall  and  humidity  is  very 
important,  for  it  is  well  known  that  scanty  rainfall  throughout  the 
year,  or  relative  dryness  of  the  air  and  soil  during  the  growing 
season,  favors  a  sparse  vegetation  and  the  development  of  xero- 
phytic  forms.  Since  vegetation  is  not  only  an  expression  of 
present  conditions,  but  to  a  greater  extent  a  record  of  conditions 
that  have  obtained  during  a  period  of  years,  and  since  the  record 
is  not  likely  to  be  altered  by  a  year  or  two  in  which  conditions 
may  depart  from  the  normal,  a  study  of  the  precipitation  in  Fig. 
2  is  instructive.  This  gives  the  mean  monthly  precipitation  at 
Pullman,  covering  a  period  of  twenty-four  years,  and  is  very 
representative  of  conditions  in  the  high  prairies.  It  may  be  seen 
at  a  glance  that  over  two  thirds  of  the  precipitation  occurs  dur- 
ing the  non-growing  season,  and  that  the  light  showers  of  July 
and  August  seldom  have  much  influence  upon  the  water  content 
of  the  soil. 

In  order  that  the  reader  may  realize  the  striking  difference  be- 

12 


Southeastern  Washington  and  Adjacent  Idaho.  13 

tween  the  distribution  of  rainfall  of  this  region  and  that  of  the 
Great  Plains  east  of  the  Rocky  Mountains,  Fig.  2  also  includes 
the  average  monthly  rainfall  at  North  Platte,  Nebraska.  It  also 
gives  the  precipitation  at  La  Crosse,  a  station  in  the  western  part 
of  the  region. 

However,  it  is  not  the  absolute  rainfall  figures  alone  which 
furnish  a  criterion  of  climate,  for  the  maximum  duration  of  the 


NORTH  PI  ffTTfffEBfl.     LUCftOSS 


FIG.  2.    Mean  monthly  precipitation  in  inches  at  Pullman  and  La  Crosse, 
Washington,  and  North  Platte,  Nebraska. 

drought  period  constitutes  a  limiting  factor  of  the  greatest  im- 
portance. 

During  the  dry  summer  months  the  sky  is  usually  cloudless. 
At  the  base  station  the  number  of  clear  days  during  the  growing 
season  (April-October)  was  68  per  cent,  for  the  years  1914  and 
1915.  Bright,  warm  days  are  followed  by  cool  nights.  In  fact, 
a  notable  feature  of  the  temperature  of  the  region  is  the  great 
variation  between  day  and  night  temperatures,  especially  in  sum- 
mer, when  a  variation  of  20°  to  40°  F.  is  not  unusual.  These 
cool  nights  naturally  indicate  rather  late  frosts  in  spring,  and 
early  ones  in  autumn.  On  the  plateau,  killing  frosts  not  infre- 
quently occur  as  late  as  the  middle  of  May,  and,  of  course,  much 
later  in  the  mountains.  In  the  fall  they  may  occur  as  early  as 
the  middle  of  September,  although  light  frosts  sometimes  occur 
in  August.  The  winters  are  mild  and  the  prairie  soils  seldom 

13 


14  A  Study  of  the  Vegetation  of 

freeze  deeper  than  4-6  inches.  The  snowfall  normally  is  about 
46  inches.  The  mean  monthly  and  annual  temperatures  at  the 
base  station  are  given  in  Table  I.  It  is  interesting  to  note  that  the 
mean  annual  isotherms  are  approximately  the  same  as  those  of 
eastern  Nebraska.  These  are  52°  F.  to  47°  F.  These  figures 
do  not  include  the  canyon  of  the  Snake  River,  which  has  a  dis- 
tinctly warmer  and  drier  climate. 

TABLE  I 
TEMPERATURES  AT  PULLMAN,  WASHINGTON 


a 

rt 

•£ 

M 

£ 

ci. 

>, 

i 
i—) 

>> 

~3 
i—  > 

ti 
9 

< 

1 

O 

1 

1 

J"i 

•<  s 

Mean  daily  maximum  

35 

22 

36 
24 

47 
3i 

56 
37 

63 

43 

72 

SO 

83 
55 

83 

54 

70 
46 

56 

38 

42 
31 

35 
24 

56 
38 

Mean  daily  minimum  

Mean  

2Q 

32 

38 

47 

S3 

59 

67 

66 

58 

49 

38132 

47 

Since  it  is  not  the  mean  temperature  of  a  region  but  rather  the 
extremes  that  exert  the  most  profound  effect  upon  plants,  Table 
I  also  includes  the  mean  daily  minimum  and  mean  daily  maximum 
temperatures. 

Another  important  climatic  factor  is  the  wind.  It  is  prevail- 
ingly from  the  southwest.  Just  as  it  has  had  such  a  profound 
effect  upon  moulding  the  topography  of  the  region,  likewise  it 
has  a  marked  effect  upon  the  vegetation.  Sweeping  across  the 
many  miles  of  open  prairie  and  desert  of  northern  Oregon  and 
south-central  Washington,  and  not  infrequently  attaining  a 
velocity  of  30-50  miles  per  hour,  it  has  a  marked  effect  upon 
the  evaporating  power  of  the  air.  By  increasing  the  latter,  it 
increases  the  saturation  deficit  and  consequently  accelerates 
transpiration.  During  the  growing  seasons  of  1913-1914,  the 
wind  blew  from  the  southwest,  or  some  southerly  or  westerly 
direction  over  60  per  cent,  of  the  time.  The  southwest  winds 
often  assume  the  form  of  dust  storms  in  summer.  For  days  the 
air  may  be  so  filled  with  dust  that  the  sun  is  scarcely  visible. 
Such  storms  may  become  serious  enough  to  cause  much  destruc- 
tion. 

Because  of  the  deficient  rainfall  and  the  low  humidity  through- 

14 


Southeastern  Washington  and  Adjacent  Idaho.  15 

out  the  region,  the  vegetational  distribution  is  markedly  influ- 
enced by  the  edaphic  and  topographic  conditions.  The  influence 
of  rainfall  upon  the  distributional  and  seasonal  activities  of  plants 
is  obviously  exerted  chiefly  through  its  power  to  replenish  soil 
moisture.  While  rainfall  is  only  indirect  in  its  relation  to  plants, 
soil  moisture  is  direct.  The  retention  of  moisture  by  soil  de- 
pends not  only  upon  the  kind  of  soil,  but  also  upon  the  slope  and 
exposure.  These  regional  differences  in  precipitation,  together 
with  topography  and  soil  depth,  delimit  in  a  more  or  less  definite 
manner  the  plant  communities. 

It  may  make  the  situation  somewhat  clearer  if,  before  taking  up 
a  detailed  discussion  of  the  structure  and  development  of  each 
vegetational  unit,  a  brief  survey  of  the  chief  plant  groups  in  the 
succession  is  given. 

GENERAL  VEGETATIONAL  DISTRIBUTION 
The  Festuca  consociation  of  the  Agropyron-Festuca  associa- 
tion occupies  the  extreme  eastern  rim  of  the  basaltic  plateau,  in- 
cluding the  lower  buttes  and  the  exposed  southwest  slopes  of 
some  of  the  higher  buttes  and  mountains  (Figs.  21  and  22) .  This 
community  extends  from  the  yellow  pine  consocies  of  the  Spo- 
kane gravels  southward  beyond  Snake  River.  It  occupies  the 
part  of  the  plateau  having  the  deepest  soils  and  the  highest  rain- 
fall. Eastward  it  reaches  to  Tekoa  Mountains,  Thatuna  Hills, 
and  other  outlying  spurs  of  the  Bitterroot  system.  The  breadth 
of  this  belt  is  variable,  depending  upon  the  precipitation  and  soil 
moisture.  Perhaps  at  no  point  does  it  exceed  40  miles.  West- 
ward and  southward  it  merges  into  the  Agropyron  consociation 
(Figs.  19  and  20). 

In  the  Festuca  consociation,  besides  the  blue  bunch-grass  (Fes- 
tuca ovina  ingrata)  and  Balsamorhiza  sagittata,  Agropyron  spica- 
tum  (including  variety  inerme)  is  the  most  important  component 
of  the  plant  cover.  In  marked  contrast  to  its  bunch  habit  in  the 
consociation  bearing  its  name,  in  the  more  mesophytic  Festuca 
community  it  is  often  a  sod  former.  Other  important  grasses  are 
Koeleria  cristata  and  Poa  sandbergii,  while  numerous  composites, 
legumes,  and  other  herbaceous  species  are  abundant.  Many  of 

15 


1 6  A  Study  of  the  Vegetation  of 

these  do  not  occur  in  the  Agropyron  community,  while  indeed 
several  species  are  confined  to  the  moist  north  hillsides  occupied 
by  this  consociation. 

At  lower  altitudes  westward  and  southward  the  well  developed 
prairie  gradually  merges  into  the  Agropyron  consociation.  Like- 
wise, on  the  rim-rock  along  the  canyons  of  streams  as  well  as  on 
dry  mountain  slopes  this  community  is  well  represented.  It  is 
characterized  by  the  definite  bunch  habit  of  its  chief  species  Agro- 
pyron spicatum.  These  bunches  are  often  more  than  8  inches 
in  diameter,  and  may  reach  a  height  of  over  3  feet.  In  addition 
to  the  absence  of  numerous  characteristically  high-prairie  species, 
and  the  more  open  nature  of  the  plant  cover,  the  Agropyron  con- 
sociation is  further  characterized  by  the  coming  in  of  certain 
plants  of  a  more  xerophytic  stamp.  Most  conspicuous  among 
these  are  the  rabbit  brush,  Chrysothamnus  nauseosus  (including 
var.  graveolens) ,  C.  viscidiflorus,  and  several  species  of  Erio- 
gonum.  The  bunch-grass  not  only  occupies  the  deeper  soils  of 
the  drier  region,  but  is  represented  in  the  scab-lands  and  on  the 
rim-rock  where  the  soils,  only  a  few  inche?  deep,  overlie  deeply 
fissured  basalt. 

On  the  unbroken  rock,  covered  with  only  an  inch  or  two  of  soil, 
Agropyron  gives  way  to  the  Poa-Polygonum  associes,  a  still  earlier 
stage  in  development  (Fig.  18).  This  latter  associes  is  well  rep- 
resented on  the  rim-rock  throughout  the  region,  as  well  as  over 
large  areas  of  the  scab-lands  westward.  The  June  grass,  Poa 
sandbergii,  Polygonum  majus,  and  Plantago  purshii,  are  the  most 
important  species.  The  knotgrass  and  plantain  play  the  role  of 
grasses  ecologically.  This  associes  is  preceded  in  the  succession 
by  communities  of  mosses  and  lichens  (Fig.  17). 

In  the  driest  part  of  the  region,  in  the  scab-land,  where  the 
basalt  is  almost  free  from  soil,  occurs  the  extreme  eastward  ex- 
tension of  the  desert  scrub  formation.  It  is  represented  by  the 
Artemisia-Atriplex  association  of  which  Artemisia,  rigida,  the 
scab-land  sage  of  the  Artemisia  consociation,  is  the  characteristic 
species  (Fig.  16).  In  the  deeper  soils  impregnated  with  alkali 
the  greasewood  consocies,  dominated  by  Sarcobatus  vermicu- 
latus,  occurs. 

16 


Southeastern  Washington  and  Adjacent  Idaho.  17 

On  the  more  mesophytic  slopes  of  the  treeless  hills  of  the  well 
developed  prairie  a  poorly  developed  shrub  associes  occurs.  This 
is  made  up  of  Symphoricarpos  racemosus,  Rosa  nutkana,  R.  piso- 
carpa,  dwarfed  specimens  of  Prunus  demissa-,  Crataegus  brevi- 
spina,  Amelanchier  spp.,  and  sometimes  Opulaster  pauciflorus, 
and  small  trees  of  Populus  tremuloides.  These  shrubs  are  better 
developed  in  the  canyons  and  are  usually  forerunners  (especially 
Opulaster  pauciflorus)  of  the  yellow  pine;  along  the  stream 
margins  they  give  way  to  the  flood-plain  forests  of  Populus, 
Crataegus,  Amelanchier,  Salix,  and  Alnus  (Fig.  35). 

On  the  outlying  buttes  as  well  as  in  the  mountains,  the  Opu- 
laster consocies  often  occupies  considerable  areas  between  the 
pines  and  the  grass  land  (Fig.  23).  It  almost  invariably  occurs 
on  the  sheltered  sides  of  lower  buttes  and  mountain  ridges,  while 
its  presence  as  a  half-dead  relict  under  the  pioneer  forest  indi- 
cates its  former  possession  of  numerous  other  situations. 

The  Prunus  consocies  is  less  abundant  than  the  preceding,  but 
it  is  well  represented  in  dry  situations  on  butte  and  mountain 
sides.  Like  Opulaster,  it  is  replaced  by  the  pines  in  the  normal 
succession.  The  chief  species  is  the  shrub-like  tree,  Prunus 
emarginata. 

On  the  higher  mountains  especially,  the  Ceanothus  consocies 
plays  a  role  similar  to  the  other  shrubs  of  this  associes.  The  two 
species  C.  velutinus  and  C.  sanguineus,  of  which  the  former  is 
the  more  important,  act  as  forerunners  for  the  yellow  pine  and 
Douglas  fir. 

The  Pinus  consocies  is  represented  by  the  western  yellow  pine, 
Pinus  ponderosa,  the  most  xerophytic  forest  tree  in  the  region. 
This  consocies  not  only  occupies  dry  slopes  and  ridges  on  the 
buttes  and  mountains,  but  has  worked  down  along  the  Palouse 
River  canyons  as  well  as  along  Rock  Lake  and  Rock  Creek  and 
Union  Flat,  to  an  altitude  of  only  1,500  feet  (Figs.  I,  24,  and  45). 
Everywhere  the  pine  is  the  pioneer  forest  tree,  and  forms  a  fring- 
ing belt  along  the  prairie.  While  it  is  usually  preceded  by  some 
shrub  consocies,  yet  it  is  able  to  invade  the  prairies,  and  especially 
those  with  a  more  sandy  soil,  without  such  an  intervening  stage. 

The  Pseudotsuga  consocies,  when  pure,  occupies  dry,  rocky 

17 


1 8  A  Study  of  the  Vegetation  of 

slopes  of  the  higher  mountains,  such  as  Gold  Hill  and  Cedar 
Mountain.  More  usually  Douglas  fir  is  mixed  with  yellow  pine, 
it  being  only  slightly  less  xerophytic  than  the  latter.  Such  mix- 
tures of  pine  and  Douglas  fir  frequently  occupy  large  areas,  the 
dominance  of  the  latter  indicating  more  mesophytic  conditions 
(Fig.  25). 

The  Larix-Abies  associes  forms  the  chief  forests  of  the  region. 
The  western  larch,  Larix  occid entails,  being  more  xerophytic  than 
the  white  fir,  Abies  grandis,  is  usually  the  first  tree  to  appear 
in  the  Pseudotsuga  consocies.  Mixed  forests  of  Douglas  fir  and 
larch  are  not  infrequent.  These  often  show  relict  pines  and  in- 
vading white  firs.  Such  exposed  situations  as  Kamiak  Moun- 
tain and  Tekoa  Mountains  are  especially  representative  (Figs.  37 
and  46). 

Likewise,  large  areas  of  sheltered  mountain  slopes  are  charac- 
terized by  Larix  and  Abies  in  nearly  equal  abundance,  with  a 
considerable  admixture  of  Douglas  fir  on  the  drier  slopes  and 
the  appearance  of  cedar,  Thuja  plicata,  in  the  moist  ravines  (Figs. 
26  and  27) .  Finally,  in  the  deep  ravines  and  most  sheltered  situa- 
tions, the  giant  cedar,  representing  the  climax  community  of  the 
region,  appears.  Often  it  forms  pure  stands  over  local  areas, 
the  low  light  intensity  excluding  other  trees  (Fig.  28).  But  more 
frequently  it  forms  a  mictium  with  the  white  fir  and  larch,  Abies 
being  the  last  to  drop  out. 

Each  stage  in  forest  succession  is  characterized  by  its  particu- 
lar group  of  shrubs  and  herbaceous  vegetation.  The  story  of 
succession  from  one  stage  to  the  next  is  largely  a  story  of  in- 
creasing water  content  and  of  decreasing  light. 

Perhaps  this  brief  survey,  together  with  a  glance  at  the  map 
(Fig.  i),  will  enable  the  reader  to  grasp  the  general  vegetational 
regions.  Following  is  an  outline  of  the  units  of  vegetation  and 
their  subdivisions  in  the  order  of  their  development. 

The  developmental  basis  for  the  analysis  of  vegetation  as  set 
forth  by  Clements  (2)  is  adopted  here.  Such  a  basis  includes 
physiognomy,  floristics,  and  habitat.  For  those  who  are  not 
familiar  with  this  basis  of  classification  a  few  words  of  explana- 
tion may  not  be  amiss. 

18 


Southeastern  Washington  and  Adjacent  Idaho. 


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2O  A  Study  of  the  Vegetation  of 

The  formation  is  the  unit  of  vegetation.  It  is  the  climax  com- 
munity of  a  natural  area  in  which  the  essential  climatic  relations 
are  similar  or  identical.  It  is  an  organic  entity,  covering  a  defi- 
nite area  marked  by  a  climatic  climax.  It  consists  of  associations 
which  are  actual  parts  of  the  area  with  distinct  spatial  relations. 

The  term  association  is  restricted  to  those  climax  communities 
which  are  associated  regionally  to  constitute  the  formation.  As- 
sociations agree  with  their  formations  in  physiognomy  and  devel- 
opment and  are  recognized  chiefly  by  floristic  differences. 

The  consociation  is  the  unit  of  the  association.  It  is  charac- 
terized by  a  single  dominant.  While  the  association  is  actually  a 
grouping,  the  consociation  is  pure  dominance.  In  the  usual  treat- 
ment, most  consociations  appear  as  associations. 

A  society  is  a  community  characterized  by  one  or  more  sub- 
dominants,  that  is  by  a  species  dominant  over  portions  of  an 
area  already  marked  by  the  dominance  of  consociation  or  associa- 
tion. It  is  a  localized  or  recurrent  dominance  within  a  dominance. 

The  above  units  of  vegetation  are  essentially  climax.  The  fol- 
lowing are  developmental.  To  ecologists  who  regard  the  forma- 
tion as  an  actual  organism,  it  is  essential  to  distinguish  develop- 
mental and  climax  communities. 

The  associes  is  the  developmental  equivalent  of  the  association. 
It  is  composed  of  two  or  more  consocies,  i.  e.,  developmental 
consociations,  just  as  the  association  consists  of  two  or  more  con- 
sociations. Like  the  association,  it  is  based  upon  life-form, 
floristic  composition,  and  habitat,  but  differs  from  it  in  as  much 
as  all  of  these  are  undergoing  constant  or  recurrent  developmental 
changes.  While  the  association  is  permanent,  in  so  far  as  de- 
velopment is  concerned,  the  associes  is  transient  although  it  may 
persist  for  many  years. 

A  consocies  is  a  developmental  community  marked  by  the  strik- 
ing or  complete  dominance  of  one  species  belonging  to  the  life- 
form  typical  of  that  stage  of  development.  It  differs  from  the 
consociation  only  in  that  it  is  a  developmental  or  serai,  while  the 
latter  is  a  climax  community. 

A  socies  is  a  serai  society  characteristic  of  a  developmental 

20 


Southeastern  Washington  and  Adjacent  Idaho.  21 

community  instead  of  a  climax  one.     Like  the  society  it  is  a  case 
of  subdominance  within  a  dominance. 

The  following  table  shows  the  relation  of  climax  and  serai  or 
development  units  to  the  formation,  as  well  as  the  relation  of 
the  units  of  each  series  to  each  other  and  the  correspondence  of 
units  in  each  series. 

FORMATION 

Climax  Units:  Serai  Units: 

Association  Associes 

Consociation  Consocies 

Society  Socies 

EVAPORATION  AND   SOIL  MOISTURE  IN  RELATION  TO 
SUCCESSION 

Without  question,  the  water  relations  of  the  habitat  are  the 
most  important  cause  of  succession.  This  is  especially  true  of 
grass  land  communities,  and  even  in  forests  where  light  is  a  con- 
trolling factor,  it  is  well  known  that  the  water  relation  has  a 
marked  effect  upon  the  tolerance  of  forest  trees.  As  Fuller  (4, 
5)  has  pointed  out,  in  a  study  of  water  conditions,  two  phases 
of  the  subject  are  of  importance. 

They  are  the  direct  source  and  amount  of  the  supply  and  the  region 
and  cause  of  the  loss.  The  latter  is  a  climatic,  the  former  largely  an 
edaphic  problem,  for  it  is  evident  that  plants  derive  their  moisture  from 
the  soil  and  lose  it  into  the  air,  and  for  the  quantitative  solution  of  these 
problems  it  is  necessary  to  measure  the  power  of  the  air  to  extract  water 
from  the  plant;  in  other  words,  the  evaporating  power  of  the  air,  and  the 
amount  of  moisture  in  the  soil  available  for  the  use  of  plants. 

Fuller  (4,  5)  and  others  have  pointed  out  that  the  evaporation 
rates  in  the  lower  aerial  stratum  and  the  range  of  water  content 
in  the  upper  subterranean  stratum  are  the  most  critical  ones. 

Within  this  (aerial)  stratum  develop  all  the  seedlings,  and  upon  their 
death  or  survival  depends  the  character  of  the  succeeding  vegetation. 
Therefore,  if  the  vegetation  of  an  association  so  affects  the  evaporation 
rate  of  this  stratum  that  it  permits  the  survival  of  seedlings  of  more 
mesophytic  species,  it  is  evident  that  a  more  mesophytic  association  will' 
develop,  and  succession  will  be  accomplished. 

Measurements  of  the  water  content  of  the  soil  and  the  evap- 

21 


22  A  Study  of  the  Vegetation  of 

orating  power  of  the  air  have  been  carried  on  in  the  various  plant 
communities  and  a  relation  has  been  established  between  the  mois- 
ture conditions  and  plant  succession. 

Livingston's  standardized  porous  cup  atmometers  were  used  to 
determine  the  rate  of  the  evaporating  power  of  the  air.  They 
were  always  placed  with  the  evaporating  surfaces  17—23  centi- 
meters above  the  surface  of  the  soil,  care  being  taken  in  all  cases 
to  select  spots  which  possessed  the  average  amount  of  herbaceous, 
shrubby,  or  tree  vegetation  characteristic  of  the  community  as  a 
whole.  These  cups  wer.e  almost  invariably  run  in  duplicate, 
sometimes  in  triplicate;  they  were  frequently  checked  and  re- 
standardized,  and  the  readings  reduced  to  those  of  the  standard 
atmometer.  In  the  following  graphs,  the  ordinates  give  the  aver- 
age daily  evaporation  during  the  intervals  indicated  by  the  ab- 
scissas. A  preliminary  report  giving  a  detailed  statement  of  a 
part  of  these  results  has  already  been  published  (16). 

Soil  moisture  determinations  were  made  at  the  same  stations 
and  at  the  same  time  that  evaporation  readings  were  taken.  In 
making  the  determinations,  samples  of  100-150  grams  were  in- 
variably taken  in  duplicate  and  from  separate  holes  about  3  feet 
apart.  These  samples  consisted  of  a  core  of  soil  to  a  depth  of  10 
inches.  They  were  dried  in  an  oven  at  a  temperature  of  100- 
105°  C.  and  the  water  content  calculated  in  percentages  on  the 
basis  of  the  dry  weight. 

In  the  following  figures,  the  results  are  represented  graphically, 
the  wilting  coefficients  being  shown  by  lines  of  the  same  type  as 
the  line  showing  the  range  of  soil  moisture  for  a  particular  com- 
munity. The  ordinates  represent  the  percentages  of  soil  mois- 
ture and  the  abscissas  indicate  the  intervals  between  readings. 
The  intervals  between  the  graphs  and  the  lines  denoting  the  wilt- 
ing coefficients  (if  these  exist  above  the  latter)  give  the  amount 
of  available  water. 

During  the  summer  of  1913  a  group  of  stations  were  estab- 
lished near  Colfax,  Washington.  Here  the  south  fork  of  the 
Palouse  River  has  cut  a  canyon  in  the  basalt  to  a  depth  of  300 
feet.  Along  the  north  bank  of  this  canyon  the  Agropyron  -con- 
sociation is  well  developed.  The  sheltered  south  bank  is  covered 

22 


Southeastern  Washington  and  Adjacent  Idaho. 


with  a  consocies  of  yellow  pine,  above  which,  and  still  on  the 
north  slope,  the  Festuca  consociation  continues.  The  atmometers 
in  the  Agropyron  community  were  installed  about  half  way  up 
the  bank  of  the  canyon.  Those  in  the  pines  were  placed  in  a 


ST 


40 


fesfa 


V  CO/  J3OCA  if  ion 


com  oc/es 


3O 


25 


ZO 


fS 


N 


N 


FIG.  3.    Evaporation  rates  in  the  Agropyron,  Festuca,  and  Pinus  communi- 
ties at  Colfax,  Washington. 

similar  position  on  the  opposite  bank,  and  about  60  feet  beyond 
these  a  station  was  established  in  the  Festuca  consociation. 
Graphs  of  the  data  from  these  instruments  have  been  plotted  in 

Fig.  3- 

These  graphs  show  a  striking  decrease  in  the  evaporating  power 
of  the  air  as  the  progressive  stages  of  vegetational  development 
are  approached.  During  1912  preliminary  measurements  indi- 
cated just  such  conditions  in  these  communities.  Stations  main- 
tained at  Pullman  during  1913,  showed  similar  differences  in 
evaporation  between  the  Agropyron  and  Festuca  consociations, 
while  during  1914  further  data  at  Colfax  confirmed  in  general 
the  above  results. 

23 


A  Study  of  the  Vegetation  of 


Fig.  4  shows  the  comparative  average  daily  evaporation  rates 
during  1913  in  the  three  communities,  respectively.     These  data 


FIG.  4.    Average  daily  evaporation  rates  in  the  Agropyron,  Festuca,  and 
Pinus  communities  during  1913. 

are  averages  of  six  stations  located  in  the  several  communities. 
The  water  content  of  the  soils  at  the  preceding  stations  at  Col- 
fax  is  indicated  in  Fig.  5.  .  A  glance  shows  that  the  soils  covered 
by  the  Agropyron  consociation  had  at  all  times  the  lowest  avail- 
able water  content.  Those  of  Pinus  and  Festuca  communities 
are  approximately  the  same,  and  indeed  this  condition  has  been 
found  to  exist  elsewhere  in  several  similar  situations.  Isolated 
determinations  at  the  same  stations  at  various  intervals  during 
the  following  season  showed  a  similar  water  content  relationship. 


KAY 


AU1US7 


c  on  SOL 


ic/f/o, 


-7  LUf 

const 


\ 


\ 


FIG.  5.     Graphs  showing  the  march  of  soil  water  to  a  depth  of  10  inches 

in  various  plant  communities  at  Colfax,  Washington. 

24 


Southeastern  Washington  and  Adjacent  Idaho.  25 

But  the  soil  water  reached  its  non-available  point  somewhat  ear- 
lier. However,  the  Agropyron  consociation  was  the  first  to  ex- 
haust its  available  supply. 

The  enormous  strain  brought  to  bear  upon  these  early  develop- 
mental plant  communities  may  be  realized  when  it  is  noted  that 
after  the  water  of  the  first  10  inches  of  soil  became  unavailable, 
the  evaporation  throughout  the  remainder  of  the  season  was  very 
high.  Two  methods  of  meeting  these  adverse  conditions  are  em- 
ployed by  plants  of  these  communities.  They  either  mature  early 
and  become  dormant  upon  the  approach  of  drought,  or  develop 
very  extensive  root-systems.  But  these  had  best  be  discussed 
under  structure  and  development  of  vegetation. 

The  mechanical  analyses  of  these  soils  show  that  those  of  the 
Agropyron  consociation  are  of  a  coarser  texture  than  those  of 
the  Festuca  consociation  (Table  II).  Likewise  the  humus  and 
volatile  matter  were  found  to  be  lower  in  the  former. 


TABLE  II 

MECHANICAL  ANALYSES  OF  SOILS  FROM  VARIOUS  PLANT  COMMUNITIES  IN 
SOUTHEASTERN  WASHINGTON  AND  ADJACENT  IDAHO 


Station 

Gravel 
Above 

2.00 

Mm. 

Fine 
Gravel 

2.00 

to  i.  oo 
Mm. 

Coarse 
Sand 

1.  00 

to  0.50 
Mm. 

Me- 
dium 
Sand 
0.50 
to  0.25 
Mm. 

Fine 
Sand 
0.25 
to  o.io 
Mm. 

Very 
Fine 
Sand 

O.IO 

to  0.05 
Mm. 

Silt 
0.05 
to  0.005 
Mm. 

Clay 
0.005 
to  o.ooo 
Mm. 

Agropyron  consociation,  Col- 
fax 

I.4O 
.80 

1.40 
.12 
3.60 

1-52 
.40 
.60 

I.OO 

.40 

.42 
.40 
1.  60 

1.08 
.90 
.60 

1.  80 
.40 

5.80 
1.72 
3-60 

7.82 
1.50 
.40 

34-48 
23.30 

26.80 

21.60 
21.65 

25.37 
33.16 

23.58 

54.20 
66.00 

54.10 
61.80 
57.60 

55.40 
53-50 

73-30 

7.04 
p.OO 

10.83 
4-34 
5.70 

4.18 
10.03 
1-49 

Festuca  consociation,  Colfax 
Festuca    consociation,    Ka- 
miak  Mt  

.68 
.60 
6.08 

3.56 

.40 

.62 

I.O4 

.40 

Pseudotsuga-Larix    commu- 
nity, Kamiak  Mt  
Thuja   consociation,    Cedar 
Mountain  
Pseudotsuga-Larix-  A  bies 
community,  Cedar  Moun- 
tain                        .            .  . 

Festuca  consociation,  North- 
east slope,  Pullman      .... 

Festuca  consociation,  South- 
west slope,  Pullman  

26 


A  Study  of  the  Vegetation  of 


A  chemical  analysis  not  only  confirms  the  low  amount  of  vola- 
tile and  organic  matter,  but  also  shows,  as  one  would  expect,  the 
low  nitrogen  content  of  the  new  soil  covered  with  bunch-grass 
(Table  III). 

TABLE  III 

CHEMICAL  ANALYSES  OF  SOILS  FROM  VARIOUS  PLANT  COMMUNITIES  IN 
SOUTHEASTERN  WASHINGTON  AND  ADJACENT  IDAHO 


Phos- 

So- 

Total 

Vola- 

Lime, 
CaO 

Pot- 
ash, 
K20 

phoric 
Anhy- 
dride, 
P205 

Soda 
Ash, 
Na20 

dium 
Tri- 
oxide, 
S03 

Solu- 
ble 
Salts 

tile  and 
Or- 
ganic 
Matter 

Insolu- 
ble 
Matter 

Hu- 
mus 

Total 

Nitro- 
gen 

Agropyron  consocia- 

tion, Colfax  

1.  08 

0.58 

0.31 

1.32 

0.034 

15.02 

5-35 

79.63 

1.  06 

0.096 

Festuca  consociation, 

Colfax  

1.27 

O.C4 

O  20 

O.47 

0  O^7 

j-j  77 

6  ~\2 

7O  OI 

2.88 

o  1  76 

Festuca  consociation, 

*••  i 

^O^T 

w*«y 

**»«|  / 

\J.\JJ  / 

^o  •  /  / 

\J  *$£• 

/v*v* 

Kamiak  Mt  

1.03 

0-45 

0.29 

O.O6 

0.047 

13.50 

5-95 

80.55 

2.77 

0.182 

Pseudotsuga  -  L  ar  ix 

community,     Ka- 

miak Mt  

0.85 

0.32 

0.41 

0.41 

0.030 

12-73 

4.95!  82.32 

1.  12 

0.081 

Thuja   consociation, 

Cedar  Mountain.  . 

LI? 

0.23 

0.59 

O.O7 

0.075 

14-77 

13.65 

71.58 

6-39 

0.399 

Pseudotsuga-L  arix- 

Abies  community, 

Cedar  Mountain  .  .  |  0.52 

0.23 

0.33 

0.03 

0.044 

14.62 

8.76 

76.62 

3.45 

0.207 

A  second  set  of  stations  was  maintained  on  Kamiak  Mountain, 
a  bold  butte  lying  9  miles  north  of  Pullman,  and  one  of  a  series 
extending  in  a  westerly  direction  from  Thatuna  Hills.  This 
butte  running  from  east  to  west  for  a  distance  of  over  2  miles, 
and  reaching  an  elevation  of  1,000  feet  above  the  surrounding 
hilltops,  is  covered  on  the  south  side  with  prairie,  while  the 
steeper  north  slope  bears  a  dense  forest  of  Douglas  fir  and  west- 
ern larch  (Figs.  36  and  37). 

On  the  south  side  trees  occur  only  near  the  summit,  where  out- 
cropping rocks  furnish  in  their  crevices  a  sufficient  shelter  and 
water  supply  for  the  establishment  of  the  seedlings.  Here  is  a 
very  open  growth  of  yellow  pine  which  flanks  the  fir  and  tamarack 
and  also  occupies  the  less  sheltered  north  base  below  the  fir- 
tamarack  community.  In  fact,  this  mountain  offered  so  many 
interesting  conditions  of  slope,  exposure,  and  vegetational  cover, 
that  13  stations  were  maintained  here  during  1913. 

26 


Southeastern  Washington  and  Adjacent  Idaho.  27 

Eight  miles  east,  near  Viola,  Idaho,  on  another  butte  slightly 
lower  than  Kamiak,  but  with  plant  communities  very  similarly 
distributed,  records  from  a  third  set  of  stations  were  obtained. 
Here  again  the  south  side  is  prairie,  which  the  pines,  occupying 
the  crest  and  northwestern  slope,  are  gradually  invading.  The 
sheltered  northeast  side  is  clothed  with  a  forest  of  Douglas  fir  and 
tamarack.  These  conditions  are  representative  of  numerous 
other  situations  (Fig.  46).  Only  as  the  mountains  become  higher 
and  rainfall  increases,  does  the  prairie  give  way  to  a  forest 
growth.  The  prairies  at  Kamiak  and  Viola  are  not  greatly  un- 
like those  upon  the  basalt  as  far  as  kinds  of  species  and  their  dis- 
tribution are  concerned,  but,  because  of  differences  in  soils  and 
greater  exposure  to  the  wind,  the  vegetation  bears  a  more  xero- 
phytic  stamp  and  there  are  fewer  plants  per  given  area,  and  con- 
sequently more  soil  surface  exposed. 

Fig.  6  gives  the  evaporation  rates  in  the  various  plant  com- 
munities on  Kamiak  Mountain,  and  also  that  of  the  pine  con- 
socies  at  Viola,  Idaho.  A  glance  at  the  chart  shows  at  once  a 
direct  relation  between  the  evaporating  power  of  the  air  and  the 
stage  in  succession.  The  station  on  Kamiak  in  the  Festuca  con- 
sociation was  on  a  south  slope  and  only  about  60  feet  below  the 
edge  of  the  pines.  The  station  in  the  pines  was  in  a  decidedly 
xerophytic  habitat,  as  is  shown  by  the  evaporation  graph,  which 
closely  follows  that  of  the  prairie.  The  ground  was  covered  with 
pine  needles  which  almost  excluded  undergrowth  and  the  at- 
mometers  were  shaded  only  indifferently  by  the  open  growth  of 
the  trees.  The  evaporation  data  in  a  more  typical  yellow  pine 
habitat  located  on  the  northwest  slope  of  the  butte  at  Viola  is 
plotted  on  the  same  chart,  for  the  sake  of  comparison.  It  corre- 
sponds in  general  with  evaporation  records  secured  from  a  second 
station  in  the  yellow  pines  located  at  the  north  base  of  Kamiak 
Mountain,  but  from  which  complete  data  were  not  obtained. 

Two  stations  were  maintained  in  the  shrub  community.  One 
of  these  was  located  on  the  south  side  of  the  mountain  and  on  a 
northeast  slope  which  was  occupied  by  a  very  typical  consocies  of 
Opulaster  pauciflorus,  into  which  the  pines  were  invading.  The 
evaporation  graph  is  given  in  the  chart.  It  may  be  noted  that 

27 


28 


A  Study  of  the  Vegetation  of 


this  station  was  intermediate  in  xerophytism,  as  expressed  by  the 
evaporating  power  of  the  air,  between  the  two  stations  in  the 
pines.  A  second  station  in  the  shrub  on  the  north  slope  of  the 
butte  and  near  the  western  end  was  maintained  in  a  dense  growth 


JLY 


A'(/G(J&T 


f/b/7 


oes 


'*  micftum 


-/    ^ 
/   /    N. 


V 


LL 


\ 


FIG.  6.    Evaporation  rates  in  the  various  plant  communities  on  Kamiak 
Mountain,  and  in  the  Pine  consocies  (graph  4)  at  Viola,  Idaho. 

of  Opulaster-Ceanothus  chaparral.  The  evaporation  rates,  not 
shown  in  the  chart,  were  much  lower,  often  being  less  than  those 
in  the  fir-tamarack  forest.  In  fact,  it  is  not  difficult  to  find  situa- 
tions in  which  shrubby  growth  is  so  dense  as  to  greatly  retard 
evaporation  and  reduce  the  light  to  a  point  where  pine  seedlings 
can  not  grow. 

28 


Southeastern  Washington  and  Adjacent  Idaho.  29 

The  station  in  the  firs  and  tamarack  on  the  north  slope  of  the 
mountain  and  only  about  60  feet  from  the  top,  was  in  a  forest  of 
nearly  pure  second  growth  Pseudotsuga  and  Larix.  These  trees 
are  mostly  about  thirty-five  years  old  and  are  equally  distributed, 
with  a  few  relict  pines  and  about  three  per  cent,  white  fir.  It 
may  be  noted  that  the  graph  of  evaporation  here  is  decidedly 
lower  than  in  any  other  habitat. 


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-  •— 

FIG.  7.     Graphs  showing  the  march  of  soil  water  to  a  depth  of  10  inches 
in  various  plant  communities  on  Kamiak  Mountain. 

The  evaporation  stations  at  Viola  gave  results  comparable  to 
those  shown  on  the  chart  for  Kamiak.  Without  exception,  the 
average  daily  rate  of  evaporation  in  the  prairie  on  the  southwest 
slope  was  higher  than  that  of  the  pines  on  the  northwest  slope. 
Likewise,  the  graph  of  evaporation  in  the  fir- tamarack  forest 
showed  a  continuously  lower  rate  than  that  in  the  pines. 

29 


30  A  Study  of  the  Vegetation  of 

At  the  stations  on  Kamiak  Mountain  where  evaporation  data 
were  obtained,  water  content  samples  were  taken  at  the  same 
intervals  of  time.  These  data  have  been  plotted  in  graphic  form 
in  Fig.  7.  The  water  content  of  the  soils  of  the  pine"  consocies 
was  obtained  from  the  station  at  the  north  base  of  the  mountain, 
that  of  the  shrub  from  the  Opulaster  consocies  on  the  northeast 
slope.  The  gradual  depletion  of  the  water  content  of  these  soils 
to  the  end  of  the  growing  season  is  characteristic.  To  fully  ap- 
preciate the  conditions  represented  on  the  chart,  a  description  of 
the  soils  is  necessary. 

A  mechanical  analysis  of  the  soils  shows  that  those  of  the 
prairie  are  somewhat  coarser  textured  than  those  of  the  fir- 
tamarack  community  (Table  II).  Likewise,  a  chemical  analysis 
of  these  two  types  of  soil  shows  that  among  other  differences 
there  is  a  markedly  lower  humus  and  total  nitrogen  content  in  the 
soils  of  the  forest  (Table  III).  This  is  due  to  fires  burning  out 
the  organic  matter. 

The  greatest  difference  in  the  soils,  however,  and  the  one  which 
most  profoundly  affects  the  vegetation  in  this  semi-arid  region  is 
their  water  holding  capacity.  An  average  of  6  tests  showed  the 
prairie  soils  on  Kamiak  had  a  water  holding  capacity  of  48  per 
cent.,  while  the  finer  soils  of  the  north  slope  which  support  a 
forest  of  fir  and  tamarack  hold  78  per  cent,  of  their  dry  weight 
of  water.  The  water  holding  capacity  of  the  soil  of  the  pine  con- 
socies was  intermediate  between  the  preceding.  We  may  com- 
pare the  soils  of  this  region  to  a  gigantic  reservoir  replenished 
mostly  during  the  non-growing  season  and  rather  thoroughly 
emptied  of  its  water  during  the  summer. 

The  actual  amount  of  water  available  to  the  forest-  and  shrub- 
covered  soils  of  the  protected  slopes  and  ravines  is  often  consid- 
erably greater  than  that  of  the  prairie.  Snow  is  blown  from  the 
wind-swept  prairie  and  deposited  on  the  sheltered  slopes.  I  have 
seen  such  drifts  20-25  feet  deep  along  the  brow  of  Kamiak  Moun- 
tain. The  late  melting  of  the  snow  makes  a  locally  late  spring 
and  consequently  shortens  the  period  of  drought  in  late  summer. 

Soil  samples  taken  on  Kamiak  Mountain  in  May  and  in  July, 
1914,  bear  out  the  conditions  found  in  the  previous  year,  but 

30 


Southeastern  Washington  and  Adjacent  Idaho.  31 

here,  as  at  Colfax,  the  available  water  was  exhausted  somewhat 
earlier  than  in  the  summer  of  1913.  On  July  14,  1914,  and  when 
the  available  moisture  of  the  surface  ten  inches  had  been  depleted 
in  all  habitats,  samples  were  taken  as  usual  at  a  depth  of  two 
feet  in  the  prairie  and  fir-tamarack  communities  respectively. 
These  showed  that  practically  no  water  was  available  even  at  this 
depth. 

The  relation  of  soil  moisture  to  plant  succession  was  likewise 
determined  at  the  stations  already  described  near  Viola,  Idaho, 
during  1913.  The  results  are  plotted  in  Fig.  8.  These  graphs 


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FIG.  8.     Graphs  showing  the  march  of  soil  water  to  a  depth  of  10  inches 
in  plant  communities  at  Viola,  Idaho. 

appear  somewhat  different  from  those  at  Kamiak.  This  is  due 
in  part  to  the  longer  intervals  between  readings.  Also  the  fir- 
tamarack  station  was  somewhat  less  mesophytic  than  that  at 
Kamiak,  but  like  the  former,  was  covered  with  a  second  growth 
of  Douglas  fir  and  tamarack.  Likewise,  the  pine  community  was 
of  a  much  more  open  type  than  that  on  the  sheltered  base  of 
Kamiak  Mountain.  The  water  holding  capacity  of  the  soil  at 


32  A  Study  of  the  Vegetation  of 

this  station  in  the  fir-tamarack  community  was  60  per  cent.,  that 
of  the  prairie  and  pines  about  45  per  cent.  On  August  14,  1914, 
the  water  content  at  each  station  was  found  to  be  somewhat 
lower  than  on  the  same  date  of  the  preceding  year.  Samples 
taken  to  a  depth  of  3  feet  in  the  prairie  showed  that  all  of  the 
available  water  had  been  used.  Indeed,  at  this  time,  practically 
all  of  the  vegetation  except  Hoorebekia  racemosa,  Solidago  mls- 
souriensis,  Carum  gairdneri,  and  a  few  other  serotinal  bloomers 
had  dried  up.  An  examination  of  the  root-systems  of  numerous 
prairie  species  shows,  however,  that  many  of  them  obtain  water 
at  much  greater  depths  than  3  feet  (Figs.  150,  i$b,  and  i$c).  In 
the  underlying  rocky  soil  on  this  butte  it  is  probable  that  consider- 
able water  was  still  available  at  this  date.  Because  of  the  rocks,  I 
was  unable  to  secure  samples  at  greater  depths  than  2  feet  in  the 
pine  community,  but  these  soils  on  August  13,  1914,  were  even 
drier  than  those  in  the  prairie.  Likewise,  the  deeper  soils  in  the 
fir-tamarack  community  were  very  dry. 

The  close  similarity  in  water  content  between  the  soils  of  the 
prairie  and  pine  communities  is  just  what  one  might  expect  when 
the  latter  consocies  was  still  quite  open  and  only  small  amounts 
of  organic  matter  had  been  added  to  the  soil.  There  is  a  close 
similarity  between  these  graphs  and  those  obtained  at  Colfax  in 
communities  of  about  the  same  stage  of  development. 

In  order  to  determine  the  relation  between  the  evaporating 
power  of  the  air  and  the  water  content  of  the  soil  in  the  cedar 
community  as  compared  with  earlier  stages  in  succession,  a  series 
of  stations  was  maintained  on  Cedar  Mountain  during  the  sum- 
mers of  1913  and  1914.  A  station  was  maintained  in  an  area  of 
the  climax  cedar  forest  which  occupied  a  north  slope  and  a  ravine 
through  which  flows  a  small  stream.  This  forest  is  over  95  per 
cent,  pure  cedar,  mostly  large  trees  from  2  feet  to  more  than  3 
feet  in  diameter.  The  rest  of  the  trees  are  large  white  firs,  most 
of  which  are  dead.  The  characteristic  undergrowth  of  meso- 
phytic  shrubs  and  herbs  need  not  be  described  here. 

About  700  feet  beyond  the  station  in  the  cedars  and  occupying 
a  slope  somewhat  above  the  latter,  a  station  in  the  fir-tamarack 
community  was  maintained.  The  Douglas  fir  and  tamarack  are 

32 


Southeastern  Washington  and  Adjacent  Idaho. 


33 


the  principal  trees,  but  a  considerable  amount  of  white  fir  and 
some  spruce  (Picea  engelmanni)  are  also  present.  The  under- 
growth is  rather  sparse. 

The  evaporation  in  the  cedar  forest  was  always  lower  than  that 
in  the  preceding  developmental  communities.  The  data  taken  in 
the  cedars  are  shown  in  Fig.  9.  Those  of  the  other  forest  sta- 


MY 


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Is 


cm  sec 


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FIG.  9.  Combined  graphs  showing  the  average  daily  evaporation  rates 
at  all  the  stations  in  the  prairie,  pine,  and  fir-tamarack  communities  on  the 
buttes  and  mountains.  The  lowest  graph  gives  the  average  daily  evapo- 
ration in  the  Thuja  consociation. 

tions  are  shown  combined  with  all  other  readings  taken  in  the 
fir-tamarack  forest.  For  the  sake  of  comparison,  the  chart  also 
gives  combined  graphs  showing  the  average  evaporation  rates  in 

33 


34 


A  Study  of  the  Vegetation  of 


the  butte-prairie  and  yellow  pine  communities.  These  data  show 
a  marked  relationship  between  the  evaporating  power  of  the  air 
and  the  stage  of  succession.  Fuller  (4,  5)  has  determined  a  simi- 
lar relationship  for  the  plant  consocies  which  culminate  in  the 
beech-maple  climax  forest.  It  is  interesting  to  note  in  this  con- 
nection that  the  evaporating  power  of  the  air  in  the  Thuja  climax 
forest  is  only  slightly  greater  (0.5  c.c.  daily  in  1913)  than  that 
of  the  beech-maple  forest  climax  of  the  East. 

In  order  to  further  check  these  results,  evaporation  readings 
were  taken  again  in  the  cedars  and  fir-tamarack  on  Cedar  Moun- 
tain during  1914.  To  this  series  of  stations  was  added  one  in  a 
very  open  yellow  pine  consocies  on  a  wind-swept  western  slope. 
The  results  are  given  in  Table  IV. 

TABLE  IV 

SHOWING  THE   AVERAGE   DAILY  EVAPORATION   RATES   IN   THE  PINE,   FIR- 
TAMARACK,  AND  CEDAR  COMMUNITIES  DURING  THE  SUMMER  OF  1914 


July  3-11      July  11-18 

July  18-25 

25-Aug.  i 

Aug.  1-7 

Aug.  7-14 

Pines  

19  c.c. 

24 

37 

35 

40 

34 

Fir-tamarack  .  .  . 

13  c.c. 

13 

20 

20 

23 

22 

Cedars  

IO  C.C. 

IO 

14 

16 

18 

I? 

A  record  of  the  water  content  of  the  soils  at  the  stations  in  the 
cedars  and  fir-tamarack  on  Cedar  Mountain  was  kept  from  June 
14  to  September  17,  1913.  During  1914  this  was  repeated  for  a 
period,  and  to  this  a  record  of  the  soil  moisture  at  the  station  in 
the  pine  community  was  added.  The  results  are  shown  graph- 
ically in  Fig.  10.  A  glance  shows  that  the  cedars  occupy  by  far 
the  most  mesophytic  habitat.  The  high  wilting  coefficient  indi- 
cates at  once  a  fine  textured  soil  with  considerable  organic  matter. 
A  mechanical  soil  analysis  (Table  II)  reveals  just  such  charac- 
teristics. This  is  in  marked  contrast  to  the  coarse  sandy  loam  of 
the  station  in  the  pine.  Likewise,  a  chemical  analysis  (Table  III) 
shows  13  per  cent,  of  volatile  and  organic  matter  in  soils  of  the 
cedar  community,  and  8  per  cent,  in  those  occupied  by  the  firs 
and  tamaracks.  The  water  holding  capacity  of  these  soils  is  re- 
markably high.  It  was  found  to  be  over  100  per  cent,  of  their 

34 


Southeastern  Washington  and  Adjacent  Idaho.  35 


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FIG.  10.    Graphs  showing  the  march  of  soil  water  in  various  plant  com- 
munities on  Cedar  Mountain. 

35- 


36  A  Study  of  the  Vegetation  of 

dry  weight.  The  chart  shows  that  at  no  time  did  these  virgin 
forests  of  fir-tamarack  or  cedar  exhaust  all  of  the  water  in  the 
surface  ten  inches  of  soil.  Likewise,  samples  at  a  depth  of  2 
feet  on  August  i,  1914,  gave  a  water  content  of  66  per  cent,  and 
19  per  cent,  in  the  cedar  and  fir-tamarack  forest  respectively. 
Similar  determinations  at  2  feet  in  the  rocky  pine-covered  soils 
gave  a  water  content  of  about  10  per  cent.,  which  is  very  near  the 
wilting  coefficient.  The  slow  growth  and  dwarfed  appearance 
of  these  trees  reflect  the  unfavorable  habitat  conditions. 

These  studies  on  the  evaporating  power  of  the  air  and  the 
amount  and  range  of  soil  moisture  in  different  plant  communities 
may  be  briefly  summarized. 

Evaporation  at  different  stations  within  the  same  plant  com- 
munity exhibits  variations  similar  both  in  character  and  degree, 
and  the  variations  in  the  rate  of  evaporation  gradually  become 
less  and  less  as  the  climax  type  of  vegetation  is  approached. 

The  great  amount  of  evaporation  in  the  earlier  stages  of  succes- 
sion seems  a  sufficient  cause  for  the  xerophytic  character  of  the 
vegetation. 

A  study  of  the  differences  of  the  rates  of  evaporation  in  the 
various  plant  communities  shows  that  these  differences  are  suffi- 
cient to  be  important  factors  in  causing  succession,  at  least 
through  the  earlier  stages,  where  light  does  not  play  an  important 
role.1 

If  sufficient  light  is  available,  there  is  no  question  but  that 
humidity  of  the  air  and  the  soil  are  the  most  important  factors 

1  While  reading  proof  of  this  manuscript  the  recent  paper  by  Gates  came 
to  the  writer's  notice.  (Gates,  F.  C.  The  relation  between  evaporation 
and  succession  in  a  given  area.  Am.  Journ.  Bot,  4:  161-178,  1917.)  As  a 
result  of  an  investigation  carried  on  at  Douglas  Lake,  Mich.,  he  concludes 
that  a  decrease  in  evaporation  is  not  a  prerequisite  to  succession ;  lowered 
evaporation  being  coincident  with  and  not  an  antecedent  to  it.  Gates 
worked  in  a  region  with  summer  rainfall,  where  the  average  daily  rates 
of  evaporation  were  low.  The  highest  average  daily  summer  evaporation 
obtained  on  open  ground  was  only  14.7  cc.  Certainly  his  conclusions  are 
not  applicable  to  a  region  of  practically  no  summer  rainfall  and  where,  in 
areas  covered  with  bunch-grass,  the  daily  evaporation  rate  for  the  whole 
growing  season  averaged  28  to  37  cc.,  with  the  average  daily  rate  for  cer- 

36 


Southeastern  Washington  and  Adjacent  Idaho.  37 

affecting  the  establishment  of  the  different  plant  communities. 
The  progressive  increase  of  the  humidity  of  the  habitat  causes 
a  corresponding  increase  in  the  mesophytism  of  the  plant  associa- 
tions. This  change  of  plant  population  from  the  xerophytic  to 
the  mesophytic  type  is  a  phenomenon  called  succession. 

The  evaporation  rates  and  the  amount  of  soil  moisture  in  the 
various  communities  vary  in  general  directly  with  the  order  of 
their  occurrence  in  the  succession,  the  climax  community  being 
the  most  mesophytic  in  both  respects. 

SOIL  TEMPERATURE  IN  RELATION  TO  SUCCESSION 
The  temperature  of  the  soil  gives  in  a  general  way  a  summation 
of  the  heat  factors  of  the  habitat.  It  combines  the  effects  of 
direct  insolation  and  radiation,  cooling  by  the  retention  of  snow 
or  by  the  evaporation  of  moisture,  and  variations  in  temperature 
caused  by  the  passage  of  currents  of  air.  Since  plant  communi- 
ties react  directly  on  temperature,  a  large  number  of  soil  tempera- 
ture readings  were  made  in  the  various  plant  communities  to  de- 
tain weeks  in  mid-summer,  even  in  well  developed  prairie,  reaching  64  cc. 
(Gates  highest  evaporation  rate  on  open  ground  for  a  single  week  is  21.6 
cc.  per  day.) 

Students  of  succession  should  keep  in  mind  that  the  evaporating  power 
of  the  air  affects  the  possibility  of  water  intake  as  well  as  water  outgo. 
High  rates  of  evaporation  rapidly  deplete  the  surface  soil  of  water  as  well 
as  desiccate  the  plant.  Mesophytes  can  not  establish  themselves  under  such 
conditions.  It  is  only  after  a  cover  of  xerophytes  cuts  down  the  great 
evaporating  power  of  the  air  in  the  stratum  in  which  seedlings  develop, 
by  shading  and  by  inhibiting  wind  movement  that  mesophytic  plants  can 
establish  themselves.  Mesophytes  do  not  replace  xerophytes  in  succession 
until  the  reaction  of  the  latter  on  the  habitat  is  such  as  to  make  possible 
the  requisite  conditions  of  soil  and  air  humidity,  ».  e.,  a  condition  where 
sufficient  water  is  available  in  the  soil  and  air,  so  that  transpiration  may 
not  exceed  absorption.  That  evaporation  is  further  reduced  by  the  meso- 
phytes  is  repeatedly  shown  in  the  preceding  data.  Conditions  for  plant 
life  are  then  less  severe  and  even  more  mesophytic  plants  can  establish 
themselves  and  become  dominant. 

This  concept  is  in  agreement  with  Fuller's  conclusion,  which  he  reached 
after  several  years  of  study  in  the  Chicago  region  (5).  Further  evidence 
is  brought  forward  in  a  recent  paper  dealing  with  the  prairie-forest  prob- 
lem in  Minnesota  and  Nebraska.  (Weaver,  J.  E.,  and  Thiel,  A.  F.  The 
Bot.  Surv.  Nebr.,  N.  S.,  i :  1-60,  1917.) 

37 


3  8  A  Study  of  the  Vegetation  of 

termine  the  relation  between  this  factor  and  succession.  Read- 
ings at  depths  of  2  and  10  inches  respectively,  were  taken  at  the 
same  stations  and  at  the  same  time  that  soil  samples  for  moisture 
determinations  were  secured.  In  addition  to  these  a  large  number 
of  readings  near  the  soil  surface,  in  the  soil  surface,  and  at  depths 
of  one  and  two  feet  respectively,  were  made  from  time  to  time. 
Many  of  the  temperature  readings  were  made  simultaneously,  and 
in  all  cases  recorded  the  interval  between  the  readings  at  the 
various  stations  was  so  short  that  the  error  thus  introduced  is 
almost  negligible.  This  possible  error  was  further  reduced  by 
taking  the  readings  in  the  various  habitats  at  any  set  of  stations  in 
varying  sequence. 

An  examination  of  these  data  shows  almost  uniformly  a  de- 
crease in  soil  temperature  as  the  climax  communities  are  ap- 
proached. The  following  tables,  selected  as  representative  from 
these  data,  are  illustrative : 


TABLE  V 

SHOWING  THE  RELATION  OF  SOIL  TEMPERATURE  TO  PLANT  SUCCESSION 
Coljax,  Wash., 


Agro- 
pyron 
Conso- 
ciation 

Ftstuca 
Conso- 
ciation 

Pinus 
Conso- 
cies 

Agro- 
pyron 
Conso- 
ciation 

Festuca 
Conso- 
ciation 

Pinus 
Conio- 
cies 

Depth,  2  Inches 

Depth,  10  Inches 

May  7  

31.0 
17-5 
22.5 
21.5 
29.0 
26.5 
28.0 
32-5 
3S-o 
20.5* 
26.5 
22.5* 

20.°C. 

21.5 
16.2 

17.5 
17.5 
19.5 
23.0 
22.5 

22.  0 
22.  0 
18.5* 
20.0 
13-0* 

8.7 
12.5 
12.5 
12.5 
13-0 
15-0 
18.0 
17-5 
18.0 
14.0 
15-0* 
15-0 
11.5* 

15-0 
19-5 
15-5* 
20.  0* 
IQ.O* 
27.0* 
25-5* 
27.O* 
29.5* 
28.0* 
22.O 
22.5 
19-5 

13-0 
15.0 
15.0* 
16.5* 
I7.O* 
19.0* 
22.0* 
24.O* 
25.0* 
20.0* 
I8.S 

18.0 
14-5 

6.0 
12.0 

I2.5* 
12.5* 
12.5* 

14.5* 

16.7* 

17.0* 

17.5* 

14.2* 
14.5 

14.0 
12.5 

9  A.  M. 

2   P.   M. 

6  P.  M. 

9:15  A.  M. 
1:30  P.  M. 
6  P.  M. 

June  6  
June  20 

June  20. 

June  20  

July  7  
July  21  

July  21  

July  21 

July  30              

August  13  

August  27  

September  10  

*  Readings  taken  at  a  depth  of  4  inches. 

38 


Southeastern  Washington  and  Adjacent  Idaho. 


39 


Kamiak  Mt.,  1912 


Festuca 
Consocia- 
tion 

Pinus 
Consocies 

Pseudo- 
tsuga- 
Larix 
Mictium 

Festuca 
Consocia- 
tion 

Pinus 
Consocies 

Pseudo- 
tsuga- 
Larix 
Mictium 

Surface 

Depth,  12  Inches 

May  3  

11.0°  C. 

27.5 

ii.  5 
21.5 

7-5 
15-5 

II.  O 

17-5 

6.0 

10.5 

9-5 
14.0 

8.0 
15-5 
13-0 
31-5 

7-0 
13-0 
10.5 
13-0 

5-0 
8-5 
7.5 
9.0 

May  12  
May  25  
June  i  

1913 


Depth,  2  Inches 

Depth,  12  Inches 

May  17  
May  24  
June  2  

10.0°  C. 
I6.5 
18.5 
24-5 
23-2 
14.2 
9-7 
17-0 

35-0 

22.0 
19.7 

25-5* 
27.O* 

21.5* 

7.5 

12.2 
14-5 
13-0 
12.5 

ii-5 
ii-S 

12.2 

17-5 

12.5 
16.5* 

16.0* 
13-2* 

5-2 
9-5 

10.2 
II.  0 

8.5 
9-5 
9.2 

IO.2 

16.0 

14.5 
10.5 

14.5* 

15.2* 

II.2* 

9-5 
15-5 
18.0 
18.0 
15-5 
12.5* 
10.7* 
16.5* 
24-5 

21.  0 

17-5* 
22.5 
23.0 

18.0 

7.0 
9-5 
H.7 
ii.  5 
10.7 

10.2* 

ii.5* 
11.7* 
14.5 

I2'.5* 

14.0 
14-5 
13-2 

5-0 
7-5 

10.2 

10.5 

8-5 
9-5* 
8.7* 
10.5* 
13-0 

ii.S 
10.5* 
12.5 
13-0 

II.  2 

June  8   

June  17  

June  26 

Tulv  2 

Tulv  i1? 

Tulv  27 

August  6         

August  15   

AugUSt  22  

August  29  

September  5  

*  Readings  taken  at  a  depth  of  4  inches. 


Viola,  Idaho,  1913 


Festuca 
Conso- 
ciation 

Pinus 
Conso- 
cies 

Pseudo- 
tsuga- 
Larix 
Mictium 

Festuca 
Conso- 
ciation 

Pinus 
Conso- 
cies 

Pseudo- 
tsuga- 
Larix 
Mictium 

Depth,  2  inches 

Depth,  10  inches 

Mav  ^ 

9.5°C. 
18.0 
16.0 

21.0 
21.  0 

23.5 
17.5 
18.5 

28.0 
25.0* 
24.0 

5-0 
10.  0 
12.0 
12.  0 
13-0 
II.  5 
12.5 
I4.O 
13-7 

16.0* 
12.7 

1-5 
10.  0 
II.  O 
II.  O 
12.  0 
II.  O 
12.0 
13.0 
II.  7 
14.0* 
1  1.0 

6.5 
13-5 
15.0 
19-5* 
20.5* 

20.0* 
I9.O 

20.  o 
19.0 

21.  0 
17-5 

4-5 
8-5 
II.  O 
II.O* 

12.5* 
ii.S* 
ii-5 
13-5 
13-0 
15-0 
13-0 

1-5 
7-5 
9.0 

II.O* 

ii.T* 

10.5* 
'0.5 

13.0 

ii-5 
13-0 

II.O 

May  24            .  . 

June  18 

June  26                          .  . 

Tulj7  10  .           .  .         ... 

July  17  ...             ... 

July  29  ...               .... 

August  8  ....           .... 

August  20  

August  30  

September  6  

*  Readings  taken  at  a  depth  of  4  inches. 

39 


A  Study  of  the  Vegetation  of 


Cedar  Mt., 


Pinus 
Conso- 
cies 

Larix- 

Abies 
Mictium 

Thuja 
Conso- 
ciation 

Pinus 
Conso- 
cies 

Larix- 
Abies 
Mictium 

Thuja 
Conso- 
ciation 

Depth,  2  inches 

Depth,  TO  inches 

July  7 

2I.O°C 
I8.5 
19-5 

iS.of 

14-5 
13-0 
12.  0 

7-5t 

13-0 
12.0 
II.  O 

6.5t 

17.0 
16.0 

21.0 

IO.O 
II.  0 

10.5 
12.5 

IO.O  • 
10.5 
9-5 
II-5 

July  18  . 

July  25  

August  i  

t  Readings  taken  at  a  depth  of  2  feet. 

A  discussion  of  light  values  as  affecting  succession  had  best  be 
given  in  connection  with  the  study  of  the  development  of  the 
forest  communities. 

THE  PRAIRIE-PLAINS  FORMATION 

The  prairies  represent  an  extreme  westward  extension  of  the 
prairie-plains  formation  east  of  the  Rocky  Mountains.1  This 
great  grass  land  area  is  here  represented  by  the  Agropyron- 
Festuca  association.  It  occupies  a  belt  of  varying  width  between 
the  desert  scrub  formation  on  the  west  and  the  Pacific  Coast  forest 
formation  on  the  east.  Thus  three  vegetational  frontiers  are  seen 
to  meet  within  the  region  covered  by  the  present  investigation. 
Altitudinally,  it  occupies  an  area  whose  westward  boundary  has 
an  elevation  of  1,200-1,300  feet,  while  eastward  it  reaches  an 
altitude  of  about  3,500  feet. 

The  prairies  are  limited  on  the  east  by  that  combination  of 
climatic  and  edaphic  factors  which  make  tree  growth  possible,  a 
type  of  vegetation  with  which  the  prairie  can  not  favorably  com- 
pete. The  changed  climatic  conditions  are  largely  due  to  in- 
creased altitude  and  are  especially  expressed  in  greater  precipita- 
tion. Likewise,  coniferous  tree  growth  is  demarked  more  or  less 

1  At  the  present  time,  I  am  not  quite  clear  whether  we  should  properly 
speak  of  the  prairie-plains  formation  or  whether,  indeed,  we  have  here  two 
grass  land  formations.  In  any  case,  the  vegetation  of  the  Agropyron- 
Festuca  association  more  nearly  simulates  that  of  the  prairies  proper, 
Agropyron  spicatum  being  an  ecological  equivalent  of  Andropogon  sco- 
parius  east  of  the  mountains. 

40 


Southeastern  Washington  and  Adjacent  Idaho.  41 

clearly  by  the  edge  of  the  great  lava  sheet.  Exceptions  to  this  are 
seen  especially  along  river  canyons  where  xerophytic  forest  trees, 
such  as  pines,  may  follow  down  the  canyons,  and  extend  out  upon 
the  basaltic  soils.  Indeed,  in  the  canyon  of  the  Palouse  River  a 
belt  of  such  woodland  extends  clear  across  the  prairie  community 
and  drops  out  only  at  an  altitude  of  1,450  feet,  and  where  it  meets 
the  desert  scrub  formation.  But  because  of  the  peculiar  rigors 
that  forest  frontiers  meet,  tree  species  invade  the  prairie  with 
extreme  slowness,  notwithstanding  the  fact  that  there  may  be 
sufficient  soil  moisture  in  such  situations  for  the  maintenance  of 
a  woodland  cover. 

On  its  lower  and  western  border  the  prairie-plains  formation 
gives  way  to  the  desert  scrub  formation.  No  sharp  geographical 
boundary  can  be  drawn  between  the  two  formations.  Under  the 
stress  of  low  available  soil  water,  the  rainfall  being  here  only  12 
to  14  inches,  soil  depth  plays  a  determining  role.  The  prairies, 
with  the  loss  of  their  less  xerophytic  components,  extend  far 
westward  and  to  lower  elevations  upon  deep  soil.  On  the  other 
hand,  the  desert  scrub  formation,  occupying  the  shallow  soils  of 
the  scab-lands  and  rim-rock,  may  extend  far  into  the  prairies. 
Indeed,  about  Rock  Lake  and  thence  eastward  along  Pine  Creek, 
the  scab-land  sage  is  represented  clear  to  the  Idaho  boundary. 
Likewise,  it  occupies  a  zone  in  the  warm  Snake  River  Canyon, 
extending  through  the  prairie  region. 

As  would  perhaps  be  anticipated  from  the  nature  of  the  transi- 
tion zone  occupied  by  the  Agropyron-Festuca  association,  its  com- 
position in  the  drier  portion  is  strikingly  different  from  that  of 
the  well  developed  upland  part.  The  latter  is  characterized  not 
only  by  a  greater  number  of  important  non-grassy  species  and  a 
denser  plant  cover  as  well  as  by  the  absence  of  certain  character- 
istic desert  plants,  but  also  by  a  change  in  habit  of  a  dominant 
grass,  Agropyron  spicatum  (including  var.  inerme),  which  under 
the  less  xerophytic  conditions  abandons  its  bunch  habit  in  part 
and  becomes  a  sod  former.  Because  of  these  differences  the 
formation  may  be  separated  into  a  more  xerophytic  part,  the 
Agropyron  consociation,  and  a  less  xerophytic  Festuca  con- 
sociation. 

41 


42  A  Study  of  the  Vegetation  of 

The  Festuca  Consociation 

This  consociation  occupies  the  larger  part  of  the  area  covered 
by  the  prairie-plains  formation.  Along  the  thin  soils  of  the 
canyons  the  ecotone  between  this  and  the  Agropyron  consociation 
is  often  very  sharp,  but  westward  and  southward  it  shades  im- 
perceptibly into  the  latter. 

The  plants  that  share  in  the  botanical  composition  of  this  con- 
sociation in  eastern  Washington  and  adjacent  Idaho  are  given 
in  the  following  lists  of  species  which  are  classified  into  three 
groups  based  upon  their  relative  abundance  and  ecological  im- 
portance. 

Composition  of  the  Festuca  Consociation 
Dominant  Species 

Agropyron    spicatum    (includ-      Festuca  ovina  ingrata 

ing  var.  inerme)2  Koeleria  cristata 

Balsamorhiza  sagittata  Poa  sandbergii 

Principal  Species 

Achillea  millefolium  lanulosa  Leptotaenia  multifida 

Astragalus  arrectus  Lupinus  ornatus 

Erythronium  grandiflorum  Potentilla  blaschkeana 

Geranium  viscosissirnum  Rosa  nutkana 

Helianthella  douglasii  Sieversia  ciliata 

Hoorebekia  racemosa  Symphoricarpos  racemosus 
Hieracium  scouleri 

Secondary  Species 

Agoseris  grandifiora  Arnica  fulgens 

Agoseris  heterophylla  Aster  fremonti 

Allium  acuminatum  Aster  laevis  geveri 

Alsine  nit  ens  Astragalus  spaldingii 

Antennaria  luzuloides  Bromus  brizaeformis 

Apocynum  pumilum  Bromus  hordeaceus 

2  The  nomenclature  in  this  paper  is  that  of  the  Flora  of  Southeastern 
Washington  and  Adjacent  Idaho,  by  C.  V.  Piper  and  R.  Kent  Beattie,  1914. 

42 


Southeastern  Washington  and  Adjacent  Idaho. 


43 


Calochortus  macrocarpus 
Carum  gairdneri 
Carex  geyeri 
Castilleja  lutescens 
Circium  foliosum 
Circium  palousense 
Claytonia  linearis 
Clematis  hirsutissima 
Cogswellia  triternata 
Collinsia  tenella 
Comandra  pallida 
Deschampsia  calycina 
Drymocallis  convallaria 
Elymus  glaucus 
Epilobium  adenocaulon 
Epilobium  angustifolium 
Epilobium  paniculatum 
Erigeron  corymbosus 
Fritillaria  pudica 
Galium  boreale 
Gaillardia  aristata 
Gentiana  oregana 
Gilia  gracilis 
Heuchera  glabella 


Hookera  douglasii 
Iris  missouriensis 
Linum  lewisii 
Lithospermum  ruderale 
Lupinus  leucophyllus^ 
Lupinus  wyethii 
Mertensia  oblongifolia 
Olsynium  grandiflorum 
Ofthocarpus  tenuifolius 
Pentstemon  confertus 
Phlox  speciosa 
Poa  ampla 

Senecio  atriapiculatus 
Sidalcea  oregana 
Silene  douglasii  multicaulis 
Solidago  missouriensis 
Synthyris  rubra 
Trillium  petiolatum 
V actinium  caespitosum 
Valeriana  edulis 
Viola  adunca 
Wyethia  ample 'xicaulis 
Zygadenus  venenosus 


The  prairies  of  eastern  Washington,  because  of  their  grassy 
verdure  and  sod-like  appearance  in  spring  and  early  summer,  gave 
rise  to  the  term  Palouse  (Fr.  pelouse,  a  land  clothed  with  a  short, 
thick  growth  of  herbage),  a  name  applied  by  the  Jesuit  mis- 
sionaries. However,  as  the  dry  summer  season  progresses  the 
prairies  become  quite  brown  and  dry,  except  on  the  steeper  north 
hillsides  and  in  the  moist  valleys.  The  south  and  southwest  slopes 
present  a  vegetational  cover  with  a  decidedly  more  xerophytic 
stamp  than  the  latter  situations.  Indeed,  this  is  so  pronounced 
that  rather  careful  and  extensive  investigations  of  the  different 
habitat  conditions  were  made.  Although  a  part  of  these  results 

43 


44 


A  Study  of  the  Vegetation  of 


have  been  published  elsewhere  (16,  17),  it  seems  well  worth  while 
considering  them  in  a  brief  manner  at  this  time. 

Two  stations  were  maintained  in  these  prairies  throughout  the 


FIG.  ii.  Evaporation  rates  on  a  southwest  slope  (solid  lines)  and  a 
northeast  slope  in  the  Festuca  consociation  during  1913  (heavy  lines)  and 
1914.  The  dotted  graph  gives  the  evaporation  rates  on  the  southwest  slope 
and  at  a  height  of  50  centimeters  during  1914. 

44 


Southeastern  Washington  and  Adjacent  Idaho.^          45 

growing  seasons  of  1913-14.  One  was  located  on  a  southwest 
slope  about  65  feet  from  the  crest  of  a  hill  somewhat  less  than  the 
average  height,  and  another  at  an  equal  distance  from  the  crest 
of  the  same  hill  and  on  an  average  northeast  slope.  The  average 
daily  evaporating  power  of  the  air  at  the  two  stations  respectively 
is  shown  in  Fig  n. 

An  inspection  of  these  graphs  shows  a  remarkable  similarity  in 
the  general  course  of  either  pair  throughout  the  season.  How- 
ever, the  difference  in  the  amount  of  evaporation  on  north  and 
south  slopes  is  just  as  striking.  During  1913  the  average  daily 
evaporation  on  the  northeast  slope  was  16  c.c.,  which  is  only  64 
per  cent,  of  that  on  the  southwest  slope  (25  c.c.).  The  season  of 
1914  was  considerably  drier  and  gave  higher  evaporation  rates  on 
both  slopes  (23.9  c.c.  on  northeast,  and  33  c.  c.  on  southwest)  with 
a  ratio  on  the  two  slopes  of  72 : 100. 

The  evaporating  power  of  the  air  on  the  southwest  slope  and  at 
a  height  of  50  cm.  is  also  shown  in  the  figure.  It  may  be  seen 
that  the  evaporating  power  of  the  air  at  this  height  is  increased 
20  to  26  per  cent,  over  that  at  17  to  23  cm.  This  factor  of  in- 
creased desiccation  plays  an  important  role  in  determining  the 
low  stature  of  many  of  the  prairie  plants.  Because  of  the  cool 
nights,  about  80  per  cent,  of  these  high  water  losses  occur  during 
the  day.  When  we  consider  that  the  daily  evaporation  in  July 
and  August  often  reaches  40  'to  55  c.c.,  and  at  a  time  when  the 
available  soil  moisture  is  depleted  to  a  depth  of  two  feet,  we  can 
see  the  necessity  for  extensive  root-systems  in  the  substratum 
as  well  as  aerial  structures  for  enduring  drought. 

The  greatest  factor  in  causing  the  differences  in  evaporation  on 
the  two  slopes  is  the  same  one  that  has  so  profoundly  influenced 
the  topography,  namely,  the  wind.  During  the  season  of  1913 
(April  1 6  to  September  3)  the  wind  was  from  a  southerly  direc- 
tion 68  per  cent,  of  the  time  and  a  total  of  13,605  miles  passed 
over  the  southwest  slope  at  a  height  of  50  cm.,  while  only  56  per 
cent,  as  many  miles  were  recorded  by  an  anemometer  similarly 
placed  on  a  northeast  slope.  In  general,  these  conditions  were 
duplicated  in  the  season  of  1914  with  the  ratio  of  100:  49.  Since 
the  factors  of  temperature,  humidity,  and  wind  movement  are 

.  45 


46  A  Study  of  the  Vegetation  of 

quite  satisfactorily  summed  up  by  measuring  the  evaporating 
power  of  the  air,  the  differences  of  temperature  and  humidity 
shown  in  the  two  habitats  need  be  discussed  only  briefly.  Al- 
though the  plant  community  reacts  directly  upon  temperature, 
humidity,  and  wind,  and  these  react  upon  each  other,  the  response 
of  the  plant  is  controlled  by  humidity. 

The  temperature  of  the  air  at  a  height  of  8  cm.  above  the  soil 
surface  as  recorded  by  thermographs  and  checked  by  a  large 
number  of  thermometer  readings  shows  a  mean  daily  range  vary- 
ing from  about  25°  F.  in  April  and  May,  to  38°  F.  in  July  and 
August.  The  daily  maximum  air  temperature  is  reached  some- 
what earlier  on  the  north  than  on  the  south  slope,  and  is  from 
2°-3°  F.  lower. 

The  steep  hillsides  are  often  in  the  shadow  long  before  the 
setting  of  the  sun.  For  long  periods  during  the  winter  months 
the  sun  does  not  strike  the  steep  north  slopes,  as  is  evidenced  by 
the  presence  of  frost,  which  may  soon  be  melted  elsewhere. 

A  continuous  record  of  humidity  kept  for  more  than  two  com- 
plete growing  seasons  shows  that  the  air  is  often  5-10  per  cent, 
drier  on  the  exposed  than  on  the  sheltered  slopes.  It  is  not  un- 
common on  dry  slopes  and  during  late  afternoons  for  the  humidity 
to  fall  to  15—20  per  cent.,  while  during  the  night  it  may  rise  again 
to  75  per  cent,  or  even  to  95  per  cent. 

These  data  on  aerial  physical  factors  show  conclusively  that 
the  plants  on  south  slopes  are  subjected  to  much  more  severe 
conditions  as  concerns  water  loss  than  those  on  sheltered  hillsides. 
Likewise  the  water  supply  of  the  former  is  usually  less  and  this 
supply  is  depleted  much  earlier  in  the  growing  season.  Before 
taking  up  the  subject  of  soil  moisture,  however,  other  important 
differences  in  the  soil  occupying  the  two  slopes  should  be  noted. 

The  wind  has  drifted  much  soil  and  humus  materials  from  the 
exposed  south  slopes  and  deposited  it  on  the  steeper  north  and 
northeast  leeward  slopes.  The  difference  in  the  mechanical  com- 
position of  the  first  foot  of  prairie  soils  on  the  two  slopes  re- 
spectively, is  shown  in  Table  II. 

The  humus  content  of  the  soils  of  north  hillsides  is  greater  at 
all  depths  to  5  feet,  in  some  cases  more  than  12  per  cent,  greater, 


Southeastern  Washington  and  Adjacent  Idaho.  47 

than  on  the  exposed  slopes,  as  was  shown  by  six  sets  of  humus 
determinations  made  for  each  foot  of  soil  on  the  two  slopes,  re- 
spectively. This  combination  of  more  clay  and  more  humus  on 
the  north  and  northeast  slopes  reflects  itself  especially  in  the 
increased  water  holding  capacity  of  the  soil.  An  average  of  six 
determinations  gave  a  mean  water  holding  capacity  of  56  per 
cent,  (based  on  dry  weight  at  104°  C.)  for  the  first  foot  of  soil 
on  north  slopes,  as  compared  with  48  per  cent,  on  south  slopes. 
This  margin  of  8  per  cent,  is  rather  an  important  difference  in 
favor  of  the  soils  on  the  protected  slopes,  since  the  wilting  coeffi- 
cients of  the  two  soils  differ  but  little.  These  substratum  differ- 


FIG.  12.  Graphs  showing  the  march  of  soil  water  to  a  depth  of  10 
inches  from  April  to  September,  1913  (heavy  lines),  and  from  May  to 
August,  1914,  on  a  northeast  slope  (solid  lines),  and  a  southwest  slope, 
respectively.  j7 


48  A  Study  of  the  Vegetation  of 

ences  are  pointed  out  here  since  it  will  be  shown  later  that  cer- 
tain plants  are  quite  confined  to  moist  north  and  northeast 
hillsides. 

Studies  of  the  water  content  of  these  soils  have  been  carried 
on  since  the  spring  of  1912.  It  will  be  unnecessary  to  burden  the 
reader  with  all  of  the  data  and  graphs  obtained,  and  only  enough 
will  be  given  to  make  plain  the  seasonal  march  of  soil  water.  In 
Fig.  12  are  graphs  giving  the  march  of  soil  water  from  April  25 
to  September  25,  1913,  on  a  typical  northeast  and  southwest  slope, 
respectively.  The  ordinates  represent  percentages  of  soil  mois- 
ture in  the  first  ten  inches  of  soil.  The  rainfall  between  the  in- 
tervals of  readings  is  also  shown  in  inches,  each  ordinate  repre- 
senting o.i  inch.  The  horizontal  solid  and  broken  lines  show 
the  wilting  coefficients  of  the  soils  on  the  northeast  and  southwest 
slopes  respectively.  The  greater  amount  of  moisture  on  the 
northeast  slope  (in  some  cases'being  twice  that  of  the  southwest 
slope)  may  be  noted  at  a  glance,  while  the  fact  that  the  soil  on 
the  exposed  slope  reached  its  wilting  coefficient  about  July  15, 
and  more  than  five  weeks  before  similar  conditions  obtained  on 
the  sheltered  slope  is  significant.  Records  for  the  fall  of  1913 
were  discontinued  when  the  rains  of  late  September  replenished 
the  parched  soil.  In  1914  these  ten-inch  soil  moisture  determina- 
tions were  made  only  at  longer  intervals  and  with  the  object  of 
determining  the  time  at  which  the  wilting  coefficient  was  reached. 
The  water  contents  on  the  dates  of  these  determinations  are  indi- 
cated by  the  light  lines,  the  solid  line  representing  soil  moisture 
on  the  northeast  slope.  The  rainfall  for  June,  1914,  being  ap- 
proximately normal  (and  not  1.6  in  excess  of  the  mean,  as  in 
1913)  the  wilting  coefficient  of  these  soils  was  reached  much 
earlier  than  in  the  preceding  year.  An  examination  of  these 
determinations,  together  with  the  rainfall  records  at  Pullman, 
shows  that  at  no  time  after  June  8  and  until  September  14,  was 
there  water  available  for  plant  growth  in  the  first  ten  inches  of 
soil  on  the  southwest  slope.  The  autumn  and  winter  rains 
replenish  the  soil  of  the  water  lost  during  the  long  period  of 
drought  and  in  the  following  spring  it  again  shows  a  maximum 
water  content. 


Southeastern  Washington  and  Adjacent  Idaho. 


49 


It  is  apparent  from  these  data  that  prairie  plants  must  obtain 
their  water  from  greater  depths  than  ten  inches,  at  least  during 
the  dry  summers.  In  fact,  some  of  these  plants  penetrate  to  a 
depth  of  12  or  13  feet,  while  most  of  them  get  the  bulk  of  their 


4' 


flugust 15 
8 — July  6- 
fluqust 15 
Jun< 


jne3 


Dec.  13 1913 


flpril  16 


flpri||8 


FIG.  13.  Graphs  showing  the  march  of  soil  water  to  a  depth  of  5  feet 
on  a  southwest  slope  from  April  18  to  August  15,  1914;  and  the  water  con- 
tent of  the  soil  on  December  13,  1913.  The  dotted  lines  indicate  water 
contents  on  a  northeast  slope. 

water  from  the  second  to  the  sixth  foot  of  soil  (Figs.  i$a,  I5&, 
and  I5c).  Consequently,  a  consideration  of  soil  moisture  at  these 
depths  is  imperative  for  a  proper  understanding  of  root  environ- 
ment. These  deeper  soil  water  determinations  (many  to  a  depth 
of  8  feet)  were  taken  at  intervals  from  December,  1912,  to 
August,  1914.  Fig.  13  (solid  lines)  shows  the  march  of  soil  water 
from  early  spring  until  late  summer  of  1914,  on  a  southwest  slope. 
It  is  apparent  that  there  was  still  a  downward  movement  of  water 

49 


5O  A  Study  of  the  Vegetation  of 

at  depths  of  4  and  5  feet  after  April  18,  but  from  June  3  to 
August  15  the  soil  moisture  was  gradually  depleted  at  all  depths 
to  5  feet.  The  heavy  horizontal  bars  give  the  wilting  coefficients 
at  the  depths  indicated.  On  July  6  no  water  was  available  in  the 
second  foot  of  soil  and  only  a  small  margin  over  the  wilting  co- 
efficient was  present  at  3  feet.  The  broken  line  indicates  that  on 
December  13  of  the  preceding  winter  the  soil  was  drier  at  three, 
four,  and  five  feet  respectively,  than  at  any  other  time  indicated. 
The  fall  rains  had  not  then  penetrated  beyond  2  feet.  While  ex- 
cavating root-systems  during  the  fall,  winter,  and  spring,  an  ex- 
cellent opportunity  was  offered  to  study  the  rates  of  penetration. 
The  wrater  penetrated  very  slowly  and  at  about  equal  rates  on  all 
slopes.  By  October  18  only  the  surface  layer  of  8  inches  was 
wetted,  and  in  late  March  the  wet  soil  reached  a  depth  of  not  more 
than  4  feet.  The  dotted  graphs  in  the  figure  indicate  the  soil 
moisture  on  the  northeast  slope. 

Aside  from  the  lower  temperature  and  greater  humidity  of  the 
north  slopes,  the  actual  amount  of  moisture  available  to  these 
soils  is  important  in  explaining  the  observed  differences  in  mois- 
ture content.  The  wind  drifts  over  to  the  sheltered  slopes  much 
snow,  which  upon  melting  adds  to  the  soil  water.  Two  examples 
will  suffice.  In  February,  1914,  exposed  prairie  slopes  had  a 
blanket  of  snow  from  5  to  8  inches  deep,  while  on  the  sheltered 
slopes  at  the  same  time  drifts  48  to  52  inches  were  measured. 
The  second,  while  an  extreme  case,  is  illustrative.  During  Feb- 
ruary and  March,  1913,  while  only  one  foot  of  snow  lay  on  the 
south  and  southwest  slopes,  the  protected  northeast  slopes  were 
covered  with  drifts  of  well-packed  snow  from  10  to  13  feet  deep. 

In  Fig.  14  is  shown  the  march  of  soil  water  similar  to  that  in 
the  preceding  figure,  but  for  soils  of  a  northeast  slope.  Here 
again,  the  downward  movement  of  water  at  3—5  feet  after  April 
18  is  apparent,  as  is  also  the  gradual  depletion  of  soil  water  at 
all  depths  to  5  feet.  Likewise,  the  broken  graph  indicates  condi- 
tions similar  to  those  explained  for  the  corresponding  graph  in 
Fig.  14.  On  August  15  no  soil  water  was  available  above  the 
two-foot  level.  If  the  graphs  in  this  figure  are  compared  with 
the  corresponding  graphs  in  the  preceding  one  it  may  be  readily 

50 


Southeastern  Washington  and  Adjacent  Idaho.  51 

seen  that  a  much  higher  water  content  was  maintained  in  the 
soils  on  the  northeast  slope. 


FIG.  14.  Graphs  showing  the  march  of  soil  water  to  a  depth  of  5  feet 
on  a  northeast  slope  from  April  18  to  August  15,  1914,  and  the  water  con- 
tent of  the  soil  on  December  6,  1913. 

In  order  to  further  check  these  deep  soil  water  conditions 
samples  were  again  taken  in  duplicate  on  the  northwest  and  south 
slopes  of  another  prairie-covered  hill.  These  findings,  indicated 
in  Table  VI,  check  very  closely  with  the  preceding,  and  the  strik- 
ing difference  between  soil  water  content  on  the  two  hillsides  at 
all  depths  is  well  shown. 

It  may  also  be  noted  that  at  each  determination  the  soil  at  any 
depth  was  drier  than  at  the  same  depth  at  the  time  of  the  preced- 
ing determination.  On  the  south  slope,  it  is  interesting  to  note 
that  without  exception,  the  soil  moisture  increased  with  depth,  and 
that  the  same  condition  maintains  in  most  cases  for  north-side  soils. 

51 


A  Study  of  the  Vegetation  of 


Thus  it  may  be  seen  that  topography  with  soil  texture  is  the  great 
middleman  that  distributes  the  soil  moisture  to  fill  the  gigantic 
earthen  reservoir,  which  again  is  largely  emptied  during  the  fol- 
lowing growing  season.  The  common  farm  practice  in  the 
Palouse  Region  of  alternating  season  after  season  the  growing 
of  wheat  with  summer  fallow,  is  a  method  of  storing  the  mois- 
ture from  one  year  for  use  in  the  growth  of  the  next  year's  crop. 

TABLE  VI 

THE  MARCH  OF  SOIL  WATER  ON  A  NORTHWEST  AND  SOUTH  SLOPE  RESPEC- 
TIVELY.   1914 


May  22 

July  6 

August  15 

o"-  6" 

N.W.                   .  . 

23.4% 

15.2 

11.6 

s  

12.5 

II.  I 

6.7 

6"  12" 

N  W 

2  C  7 

I"?  7 

12   I 

S  

17.9 

II.4 

10.2 

At    2' 

N  W 

27  o 

18.9 

II.  8 

S 

IQ.Q 

12.6 

10.2 

At    V 

N  W. 

30.2 

23.7 

14.4 

S 

20.  2 

13.2 

10.6 

At    4' 

N.W.                     .  .    . 

27.2 

24.9 

18.0 

S.                 

22.0 

17.3 

10.5 

At    5' 

N.W  

24.3 

21.3 

19.5 

S  

22.4 

19.6 

12.3 

The  differences  in  soil  temperature  on  the  two  slopes  and  at 
various  depths  may  be  briefly  noted  here.  Table  VII  gives  the 
soil  temperature  at  a  depth  of  3  inches  on  the  two  slopes  respec- 
tively, for  three  representative  days  in  July,  1914.  The  higher 
temperature  prevailing  on  the  south  slope  as  well  as  the  greater 
range  in  temperature  is  very  marked. 

TABLE  VII 
SOIL  TEMPERATURE  AT  A  DEPTH  OF  3  INCHES 


Station 

Minimum 

Time 

Maximum 

Time 

Range 

Day 

N.E.  slope  ..... 
S.W.  slope  
N.E.  slope  
SW  slope 

63.5°  F. 
67.0 
59-0 
68.0 

A.  M. 

5 
7 
5 
7 

75-0 
93-o 
7i-S 
94.0 

P.  M. 
3 

4 
3 

4 

II.  S 
26.0 
ii.  5 
26.0 

July  27 
July  27 
July  28 
July  28 

N  E.  slope 

61.0 

5 

73-5 

3 

12.5 

July  29 

S.W.  slope  

67.0 

7 

95-o 

4 

26.0 

July  29 

52 


Southeastern  Washington  and  Adjacent  Idaho. 


53 


A  comparison  of  a  large  number  of  temperature  readings  at 
one  foot  on  the  two  slopes  reveals  the  fact  that  at  this  depth  the 
soils  on  the  south  slopes  are  from  3°  to  5°  F.  warmer  in  early 
spring  than  those  on  the  north  slopes  and  that  these  differences 
may  increase  by  late  summer  to  7°-io°  F.  In  Table  VIII  the 
soil  temperature  from  i  to  5  feet  on  the  two  slopes  at  the  base 
station  is  given. 

TABLE  VIII 

SOIL  TEMPERATURE  AT  1-5  FEET  ON  APRIL  18  AND  AUGUST  15,  1914,  ON  A 
NORTHEAST  AND  SOUTHWEST  SLOPE,  RESPECTIVELY 


Depth 

April  18 

August  15 

N.E. 

S.W. 

N.E. 

S.W. 

I  foot  

45-7  °F. 
45.  i 
45-0 
45-0 
45  -o 

50.3 
So.o 

48.2 
47.0 
46.4 

65.0 
61.7 
58.0 
57-2 

54-5 

73-0 
70.0 
66.2 
64.4 
62.6 

2  feet  

3  feet  

4  feet    

5  feet  

The  higher  soil  temperature  prevailing  on  the  south  slopes 
has  much  to  do  with  the  earlier  seasonal  activities  of  many 
plants  here  than  of  those  on  north  hillsides. 

Summarizing  briefly  the  habitat  conditions  in  the  prairie,  we 
find  the  north  and  northeast  slopes  less  xerophytic  than  the  south 
and  southwest  slopes.  This  is  due  in  part  to  actually  greater 
precipitation  caused  by  blowing  snow,  and  in  part  to  soil  texture, 
which  is  more  open,  has  more  humus,  and  a  greater  water  hold- 
ing capacity.  These  factors  are  reflected  in  the  greater  amount 
of  soil  water  and  in  lower  temperatures.  Likewise,  these  slopes 
are  sheltered  from  the  drying  southwest  winds,  and  from  the 
perpendicular  rays  of  the  sun.  This  is  reflected  in  slightly  lower 
air  temperature  and  greater  humidity,  and  especially  in  the  lower 
evaporating  power  of  the  air. 

These  differences  in  habitat  are  reflected  in  the  vegetational 
cover  in  a  number  of  ways.  The  resumption  of  growth  in  late 
March  or  early  April  is  often  from  10  to  17  days  earlier  on  the 
warmer  exposed  slopes.  Likewise,  the  same  species  flower  and 
dry  up  correspondingly  earlier  than  on  the  sheltered  slopes.  The 
vegetational  cover  is  less  dense  on  the  exposed  slopes,  often  10  ta 

53 


54  A  Study  of  the  Vegetation  of 

30  per  cent,  of  the  ground  appearing  bare  by  mid-summer.  Closer 
investigation,  however,  reveals  that  much  of  this  space  was  for- 
merly occupied  by  prevernal  and  vernal  plants  which  have  by  this 
time  become  dry  and  brown.  However,  relict  xerophytic  mosses 
and  lichens  indicate  the  more  open  nature  of  the  ground  cover. 

A  careful  census  of  the  plant  population  consisting  of  scores  of 
list  quadrats  reveals  striking  differences,  not  only  in  the  number 
of  individuals,  but  also  in  the  floristic  distribution  of  species. 
On  an  average  it  was  found  that  south  slopes  are  clothed  with 
about  115  individuals  per  square  meter,  while  the  north  slopes, 
with  only  about  3  per  cent,  of  unoccupied  soil  space,  showed 
more  than  200  individuals  in  the  same  unit  area. 

Perhaps  the  most  pronounced  difference  is  the  smaller  number 
or  total  absence  of  more  mesophytic  plant-forms  which  thrive  in 
moist  situations.  Erythronium  grandiflorum,  Trillium  petiola- 
tum,  Capnorea  villosula,  Vaccinium  caespitosum,  and  Viola 
adunca  are  examples  of  species  characteristic  of  moist  north  hill- 
sides. Numerous  species,  such  as  Sidalcea  oregana,  Circium 
foliosum,  Valeriana  edulis,  Gentiana  oregana,  and  others  seldom 
occur  on  south  slopes. 

The  blue  bunch-grass,  Festuca  ovina  ingrata,  ranking  in  im- 
portance with  Agropyron  spicatum,  is  the  most  characteristic 
grass  of  the  region  (Fig.  48).  The  slightly  pale-green  plants  are 
densely  tufted  into  bunches  from  I  to  4  inches  in  diameter.  The 
low,  bushy,  setaceous  leaf  blades  scarcely  exceed  a  height  of  12 
inches.  It  is  not  unusual  to  find  as  many  as  10  to  13  of  these 
bunches  in  a  single  square  meter.  The  bunch  habit,  an  aspect 
of  prairie  vegetation  which  is  found  more  or  less  developed  in 
practically  all  prairie  regions,  and  one  which  has  succeeded  in  a 
remarkable  degree  in  withstanding  xerophytic  conditions,  is  most 
pronounced  on  the  drier  slopes.  In  moist  situations  the  clumps 
are  smaller,  but  I  have  never  found  Festuca  producing  rhizomes. 
Like  the  other  prairie  grasses  Festuca  flowers  by  the  middle  of 
June.  Since  its  root-system  draws  the  water  supply  from  the 
upper  1 8  inches  of  soil,  its  drying  out  in  July  and  resumption  of 
growth  upon  the  arrival  of  the  autumn  rains  can  easily  be  ac- 
counted for. 

54 


Southeastern  Washington  and  Adjacent  Idaho.  55 

The  June  grass,  Poa  sandbergii,  one  of  the  pioneers  of  herba- 
ceous vegetation  in  the  moss  consocies,  is  also  perhaps  one  of  the 
most  important  interstitial  plants  of  the  prairies.  It  grows  in 
small  tufts  usually  only  about  0.5  to  1.5  inches  in  diameter  but 
as  many  as  30  to  40  of  these  may  occur  in  a  single  minor  quadrat 
between  the  bunches  of  Festuca  and  Agropyron.  It  is  called 
June  grass  because  of  its  habit  of  flowering  in  May  or  early  June 
and  remaining  dormant  until  the  advent  of  the  fall  rains.  This 
means  of  evading  drought  is  necessitated  by  its  very  shallow 
root-system,  which  seldom  exceeds  8  inches.  Its  xerophytic 
tendencies  are  shown  by  its  less  abundance  in  mesophytic  situa- 
tions. 

The  sod-forming  habit  of  Agropyron  spicatum  in  the  prairies 
of  eastern  Washington  is  in  marked  contrast  to  its  well  developed 
bunch  habit  on  the  rim-rock  or  in  the  shallower  and  drier  soils 
westward.  I  have  found  the  soil  quite  filled  with  rhizomes  of 
considerable  length  connecting  smaller  clumps  of  this  grass. 
It  may  well  abandon  this  marked  xerophytic  character,  for 
its  long  roots  extend  into  the  fourth  and  fifth  foot  of  soil,  and 
tap  the  earthen  reservoir  far  below  the  root  limits  of  competing 
grass  species. 

Another  common  bunch-grass,  which,  with  the  three  preceding, 
completes  the  list  of  dominant  grass  species,  is  Koeleria  cristata. 
Like  Poa,  the  bunches  are  often  small,  but  numerous.  It  com- 
pletes flowering  in  early  July  and  remains  dormant  until  revived 
by  the  autumn  rains.  Its  well  developed  but  short  root-system 
gets  water  from  the  first  15  inches  of  soil  only. 

The  entire  absence  of  late  blooming  grasses,  such  as  An- 
dropogon,  Sorghastrum,  Bouteloua,  and  others  of  the  prairie- 
plains  region,  may  be  accounted  for  by  the  peculiar  distribution 
of  the  precipitation. 

A  most  characteristic  plant  of  the  prairies,  and  one  which  for 
a  time  often  outranks  the  grasses,  is  the  prairie  sunflower,  Bal- 
samorhiza  sagittata  (Fig.  42).  Its  abundance,  size,  and  duration 
all  unite  to  make  it  a  very  important  ecological  species.  It  is  not 
unusual  to  find  a  dozen  of  these  plants  in  an  area  of  four  square 
meters.  Only  on  the  steeper  northeast  slopes  and  moist  valleys 

55 


56  A  Study  of  the  Vegetation  of 

is  it  absent.  A  medium-sized  mature  plant  occupies  an  area  of 
4-5  square  feet ;  it  may  have  as  many  as  50-80  of  the  large  sagittate 
leaves  and  a  total  transpiring  surface  of  30  square  feet.  From 
the  short,  thick,  multicipital  stem  (I  have  counted  39  individual 
leafy  shoots  on  a  stem  9  inches  in  diameter)  the  new  leaves  appear 
in  April.  By  the  first  of  May  the  plant  is  often  in  full  bloom. 
Then,  with  its  large,  yellow  flowers,  it  is  the  most  conspicuous  ob- 
ject of  the  vernal  aspect,  which  lasts  until  about  June  I.  After  this 


FIG.  15°.  This  and  the  two  following  figures  (15*  and  15°)  are  bisects 
showing  the  root  and  stem  relations  of  important  prairie  plants.  These 
figures  were  drawn  from  photographs  and  from  data  obtained  by  the 
excavation  and  examination  of  325  root-systems-  of  these  eighteen  species. 
H,  Hieracium  scouleri.  K,  Koeleria  cristata.  B,  Balsamorhiza  sagittata. 
F,  Festuca  ovina  ingrata.  G,  Geranium  viscosissimum.  P,  Poa  sandbergii. 
Ho,  Hoorebekia  racemosa.  Po,  Potentilla  blaschkeana. 

the  whole  aerial  part  dries  up,  but  the  dead  leaves  are  conspicuous 
throughout  the  year.  It  has  a  strong,  woody  tap-root,  sometimes 
reaching  a  diameter  of  4  inches,  which  may  penetrate  into  the  soil 
for  a  distance  of  8  feet.  Not  only  is  it  deep-rooted,  but  the  ex- 
tensive and  wide-spreading  laterals  lay  hold  upon  a  very  large 
area  of  soil. 

In  another  place  will  be  found  a  detailed  report  of  a  study  of 

56 


Southeastern  Washington  and  Adjacent  Idaho. 


57 


the  root-systems  of  many  of  the  most  important  prairie  plant 
species  and  it  is  there  pointed  out  that  the  response  of  many  of 
the  plants  to  severe  environmental  conditions  is  met  by  well  de- 
veloped and  extensive  root- systems  (17).  Figs.  i$a,  i$b,  and 
15^  show  in  part  the  results  of  these  investigations  as  regards 
root  type  and  depth  of  penetration. 

Standing  well  above  most  other  prairie  vegetation  and  con- 
spicuous not  only  for  its  size  but  also  often  for  its  great  abun- 
dance is  Leptotaenia  multifida.  This  large,  much  branched,  un- 
belliferous  plant  occurs  quite  commonly  on  both  dry  and  moist 


FIG.  I5&.  S,  Sieversia  ciliata.  W ,  Wyethia  ample  xicaulis.  L.  I,  Lupinus 
leucophyllus.  L.  o,  Lupinus  ornatus.  P,  Poa  sandbergii.  L,  Leptotaenia 
multifida.  A,  Agropyron  spicatum. 

hillsides.  It  often  characterizes  rather  large  areas,  but  even  if 
occurring  sparsely  it  is  nevertheless  very  conspicuous  and  espe- 
cially in  June,  when,  after  flowering,  the  leaves  turn  yellow  be- 
fore drying  up. 

Erythronium  grandiflorum  constitutes  a  well-marked  prevernal 
aspect  society  on  moist  north  hillsides  from  early  April  to  the  first 
week  in  May.  Even  before  the  plants  open  their  large  golden 

57 


58  A  Study  of  the  Vegetation  of 

yellow  blossoms,  their  great  numbers,  often  more  than  100  indi- 
viduals in  a  square  meter,  give  a  distinct  tone  in  contrast  to  the 
gray  background  of  dead  vegetation. 

Later  on  by  the  blossoming  of  Amelanchier,  Crataegus,  Prunus, 
and  Rosa  especially,  the  developmental  shrub  community  be- 
comes very  conspicuous.  But  the  prairies  become  veritable 
flower  gardens  during  the  month  of  June.  Then  the  large  red 


FIG.   15°.    Hu,  Heuchera  glabella.     A,  Astragalus  arrectus.     S,  Sidalcca 
oregana.    H,  Helianthella  douglasii.    Ag,  Agropyron  spicatum. 

blossoms  of  Geranium  and  Rosa  mingle  with  the  yellow  of  Poten- 
tilla,  Gaillardia,  Castilleja,  and  Helianthella.  Senecio,  Astragalus, 
Arnica,  and  societies  of  Wyethia  brighten  the  landscape  with  their 
yellow  blossoms,  while  the  tall,  widely  spaced,  sentinel-like  plants 
of  Cirsium  foliosum  with  their  showy  red  flowers  add  pleasing 
variety. 

Likewise  the  purple  flowers  of  various  lupines  are  conspicuous. 
Lupinus  wyethii  is  only  locally  abundant.  It  is  especially  no- 
ticeable in  the  vernal  aspect.  It  often  covers  areas  of  the  driest 
hillsides  and  the  whole  aerial  part  dries  up  early.  Lupinus  or- 
natus  is  very  cosmopolitan  over  the  high  prairies  and  is  an  im- 
portant species.  Lupinus  sericeus  is  confined  to  the  warmer 

58 


Southeastern  Washington  and  Adjacent  Idaho.  59 

valleys  southward  and  westward.  Here  its  size  and  abundance 
make  it  an  important  floral  component.  Lupinus  leucophyllus 
is  the  most  mesophytic  of  the  group  and  is  found  at  home  typ- 
ically on  moist  north  slopes  or  in  the  valleys. 

In  the  lower  ground  considerable  areas  are  given  tone  by  the 
white  flowers  of  Galium.  But  with  the  increasing  stress  of 
drought  the  aestival  aspect  passes,  lingering  only  in  moister  situa- 
tions. Then  the  leaden  landscape  of  dry  balsam-root,  drying 
grasses,  and  silvery-leaved  lupines  and  hawkweed  is  relieved  only 
by  the  yellow  and  the  blue  of  sparsely  spaced  goldenrods,  asters, 
and  Hoorebekia. 

I  have  described  very  briefly  the  well  developed  prairie  repre- 
sented by  the  Festuca  consociation.  Westward  and  southward 
as  the  altitude  decreases  and  the  rainfall  is  correspondingly  less, 
many  important  species  either  become  fewer  in  individuals,  or 
are  found  only  in  the  most  mesophytic  situations,  or  indeed  dis- 
appear entirely.  Among  these  the  following  may  be  enumerated : 

Astragalus  arrectus  Leptotaenia  multifida 

Carex  geyeri  Lithospermum  ruderale 

Cirsium  foliosum  Potentilla  blaschkeana 

Drymocallis  convallaria  Rosa  nutkana 

Gaillardia  aristata  Rosa  pisocarpa 

Galium  boreale  Sidalcea  oregana 

Geranium  viscosissimum  Sieversia  ciliata 

Helianthella  douglasii  Symphoricarpos  racemosus 

Heuchera  glabella  Trillium  petiolatum 

Hieracium  scouleri  Viola  adunca 

Hoorebekia  racemosa  Wyethia  amplexicaulis 

The  Agropyron  Consociation 

This  community  in  an  early  stage  of  development  covers  hun- 
dreds of  acres  of  the  thin  soil  in  the  scab-lands.  The  characteris- 
tic plant  is  Agropyron  spicatum.  Areas  characterized  by  this 
consociation  are  peculiar  because  of  the  growth  form  of  the  domi- 
nant species  as  well  as  a  number  of  the  commoner  interstitials 
which  show  various  degrees  of  the  same  bunch  habit.  Numerous 

59 


60  A  Study  of  the  Vegetation  of 

other  plants  are  mat-formers,  while  a  few  are  more  or  less 
shrubby  in  character. 

The  bunches  of  Agropyron  are  often  1-2  feet  apart,  perhaps 
only  2-5  occurring  in  a  square  meter  (Fig.  47).  The  individual 
bunches  or  tufts  are  composed  of  from  100-350  or  more  stiff, 
erect  stems,  reaching  a  height  of  2-3  feet.  Several  generations 
of  dead  stems  are  to  be  seen  in  these  persistent  bunches,  the  old 
leaves  and  culms  forming  a  tangle  at  the  bushy  base.  Conse- 
quently the  landscape  appears  just  as  characteristic  in  late  sum- 
mer when  this  dominant  is  drying  out  as  in  the  fall  when  it  takes 
on  renewed  growth,  or  in  early  spring  when  a  host  of  inter- 
stitials  for  a  time  cover  the  ground  with  a  green  carpet.  Agro- 
pyron is  the  one  grass  best  adapted  for  such  situations.  Its  well 
developed  roots  penetrate  the  moist  crevices  in  the  underlying 
basalt  to  a  depth  of  4  or  5  feet. 

Grasses  like  Festuca  ovina  ingrata  and  Koeleria  cristata  with 
rather  short  root-systems  find  this  an  uncongenial  habitat.  How- 
ever, a  few  grasses  with  very  short  root-systems  and  an  early 
blooming  habit  are  very  successful  interstitials.  Of  these,  Poa 
sandbergii  and  the  low  annual,  Festuca  pacifica,  are  by  far  the 
most  important.  Hundreds  of  individuals  of  the  latter  fre- 
quently occur  in  a  single  square  meter.  Mats  of  Antennaria 
dimorpha  and  dense  growths  of  Plantago  purshii  are  likewise 
common  between  the  scattered  bunches  of  the  dominant.  These 
interstitials,  together  with  numerous  others  are  quite  as  common 
in  the  preceding  Poa-Polygonum  associes  of  which  this,  indeed, 
except  'for  the  dominance  of  Agropyron,  might  be  considered  a 
late  developmental  stage.  However,  the  presence  of  the  rabbit 
brush,  Chrysothamnus  nauseosus,  C.  viscidiflorus,  Tetradymia 
canescens,  Erigeron  hispidissimus,  and  various  lupines,  espe- 
cially in  pockets  of  deeper  soil,  indicates  the  developmental  trend 
toward  the  more  typical  Agropyron  community. 

In  the  deep  soils  of  the  hills  bordering  the  scab-lands  the  Agro- 
pyron consociation  is  better  developed  (Fig.  20).  The  appear- 
ance of  Festuca  ovina  indicates  more  favorable  life  conditions. 
Indeed,  the  latter  sometimes  assumes  equal  importance  with 
Agropyron  on  the  more  moist  slopes.  But  the  larger  amount  of 

60 


Southeastern  Washington  and  Adjacent  Idaho.  61 

unoccupied  soil  surface,  from  30  to  40  per  cent.,  and  the  appear- 
ance of  several  new  species  of  a  decidedly  xerophytic  stamp  gives 
this  consocies  quite  a  different  physiognomy  from  the  well  de- 
veloped prairies  eastward.  The  following  lists  indicate  the 
dominant,  principal,  and  secondary  species : 

Composition  of  the  Agropyron  Consociation 

Dominant  Species 
Agropyron  spicatum 

Principal  Species 

Achillea  millefolium  var.  lanu-  Festuca  ovina  ingrata 

losa  Lupinus  ornatus 

Chrysothamnus  nauseosus  Lupinus  sericeus 

Chrysothamnus  nauseosus  gra-  Poa  ampla 

veolens  Poa  sandbergii 

Chrysothamnus  viscidiflorus  Tetradymia  canes c ens 

Festuca  pacifica 

Secondary  Species 

Agoseris  heterophylla  Epilobium  paniculatum 

Allium  acuminatum  Erigeron  corymbosus 

Alsine  nit  ens  Erigeron  hispidissimus 

Antennaria  dimorpha  Eriophyllum  lanatum 

Artemisia  rigida5  Gilia  pharnaceoides 

Astragalus  collinus  Koeleria  cristata 

Astragalus  spaldingii  Lupinus  wyethii 

Balsamorhiza  sagittata  Madia  exigua 

Carex  filifolia  Madia  glomerata 

Cirsium  undulatum  Phlox  longifolia 

Clarkia  pulchella  Plantago  purshii 

Cogswellia,  triternata  Potentilla  biennis 

Elymus  condensatus  Stipa  comata 

The  rabbit  brush,  although  more  common  westward,  is  an  abun- 
dant and  conspicuous  component  of  the  bunch-grass  community, 
a  Relict 

61 


62  A  Study  of  the  Vegetation  of 

Its  shrubby  growth-form,  numerous,  erect,  fascicled,  and  dense, 
white-woolly  branches  and  white-woolly  leaves,  combined  with  a 
greater  height-growth  than  most  of  its  associates,  make  it  a  con- 
spicuous plant  in  the  landscape.  The  non-woolly  variety,  Chryso- 
thamnus  nauseosus  graveolens,  not  less  conspicuous,  is  also  very 
abundant.  Both  plants  extend  well  up  the  warm  valleys  and 
canyons  but  are  practically  absent  from  the  high  prairies  eastward. 

Tetradymia  canescens,  with  a  growth  form  similar  to  the  pre- 
ceding half-shrubs,  likewise  lends  a  decidedly  xerophytic  tone  to 
the  dry  scab-lands.  It  reaches  its  eastward  extension  in  this 
region. 

A  plant  which  forms  a  rather  distinct  consocies  is  Elymus 
condensatits.  On  moist  flood-plains  this  grass  reaches  a  height 
of  3-5  feet.  In  such  situations  the  stout  stems  are  densely 
tufted  and  areas  of  many  acres  may  be  dominated  by  this  species. 
In  deep  soils  on  the  dry  hillsides  it  is  not  infrequent,  but  here  it 
usually  occurs  in  more  or  less  isolated  clumps. 

In  the  eastward  extension  of  the  Agropyron  community  along 
the  rim-rock  of  the  streams  into  higher  altitudes,  many  of  the 
species  being  confined  to  the  warmer  valleys,  drop  out.  In  such 
situations  Balsamorhiza  sagittata  is  often  abundant  between  the 
bunches  of  Agropyron. 

In  conclusion  it  may  be  said  that  the  plants  of  this  consocies 
live  typically  not  only  in  a  climate  of  lower  rainfall  but  also  one  in 
which  the  period  of  drought,  owing  to  the  warmer  climate  with  a 
growing  season  several  weeks  earlier,  is  correspondingly  increased 
as  compared  with  that  of  the  well  developed  prairies  of  the 
higher  altitudes. 

In  the  preceding  pages  I  have  treated  the  Festuca  and  Agro- 
pyron communities  as  climax  units  of  vegetation.  Without  ques- 
tion, favorable  changes  of  climatic  conditions,  such  as  a  slight  in- 
crease in  rainfall,  would  cause  an  extension  of  the  Festuca  com- 
munity into  the  area  now  occupied  by  the  Agropyron  consocia- 
tion. The  latter  in  turn  would  extend  its  area  downward  and 
westward  into  the  desert  scrub  formation.  Indeed,  such  move- 
ments of  plant  populations  are  easily  traced  in  the  new  areas  of 
rim-rock  and  scab-land  where  they  are  brought  about  as  a  result 

62 


Southeastern  Washington  and  Adjacent  Idaho.  63 

of  favorable  modifications  of  the  edaphic  conditions  such  as  an 
increase  in  amount  or  an  increase  of  the  water  holding  capacity 
of  soils. 

Likewise,  on  its  high  eastern  border  the  Festuca  consociation 
contains  a  potential  shrub  community.  Almost  everywhere  Sym- 
phoricarpos,  Rosa,  and  Spiraea  are  present  but  are  held  in  check 
by  competing  herbs  and  grasses.  A  local  disturbance  of  the 
habitat  such  as  the  building  of  a  fence  or  the  burrowing  of  squir- 
rels modifies  it  favorably  by  increasing  the  water  holding'capacity 
of  the  soil  and  swings  the  balance  in  favor  of  the  shrubs.  Once 
established  the  shrubs  may  furnish  a  suitable  nursery  for  seed- 
lings of  the  yellow  pine  and  thus  the  prairie  may  give  way  to 
forest.  These  modifications  of  edaphic  conditions  foreshadow 
those  which  would  be  caused  by  a  favorable  swing  of  climate, 
while  the  reverse  of  these  conditions  would  follow  an  unfavor- 
able change.  Indeed,  the  balance  between  prairie,  shrub,  and 
forest  is  so  nicely  adjusted  that  even  a  few  years  of  exceptionally 
dry  or  unusually  wet  weather  would  be  recorded  in  the  movements 
of  the  vegetation. 

The  serai  stages  of  the  Agropyron-Festuca  association  will  next 
be  considered,  and  in  this  place  we  shall  discuss  those  of  the 
xerosere  only.  This  will  be  followed  by  a  brief  treatment  of  the 
desert  scrub  formation,  after  which  the  xerosere  will  be  traced  to 
its  culmination  in  the  climax  cedar  forest. 

(See  outline  of  vegetational  units,  page  19.) 

LICHEN-MOSS   COMMUNITIES 

Where  the  basaltic  rock  is  exposed  along  the  canyon  walls  and 
in  the  scab-lands,  as  well  as  upon  outcropping  ledges  of  crystalline 
rocks  on  buttes  and  mountains,  a  flora  of  lichens  and  mosses 
abounds.  During  the  dry  summer  months  the  rocks  appear  quite 
bare  and  devoid  of  vegetation,  but  upon  the  advent  of  the  autumn 
rains,  not  only  lichens  and  mosses,  but  also  the  June  grass,  which 
closely  follows  the  latter  in  point  of  succession,  takes  on  renewed 
growth.  Then  these  situations,  with  their  new  verdure,  become 
quite  inviting.  Three  associes  are  easily  distinguishable,  of  which 
that  dominated  by  various  crustose  lichens  is  the  pioneer. 

63 


64  A  Study  of  the  Vegetation  of 

Composition  of  the  Rhizocarpon-Lecidea  Associes 

Dominant  Species 
Rhizocarpon  geographicum  Lecidea  lapicida 

Principal  Species 

Acarospora  chlorophana  Lecidea  fuscocinerea 

Blastenia  ferruginea  Rinodina  oreina 

Lecanora  calcarea 

Rhizocarpon  geographicum  is  by  far  the  most  abundant  and 
widely  distributed  species.  It  occupies  the  most  exposed  situa- 
tions and  forms  a  well  defined  consocies.  The  greenish-yellow 
color  of  the  rocks  is  due  to  its  presence.  The  characteristic 
checking  of  the  dry  thallus  undoubtedly  aids  greatly  in  the  ab- 
sorption of  water. 

Lecidea  lapicida  often  covers  areas  of  several  square  inches  ex- 
clusively. Like  Rhizocarpon  it  is  of  sufficient  abundance  and  im- 
portance to  be  ranked  as  an  associes.  On  the  quartzite  rocks 
Rinodina  oreina  often  replaces  Rhizocarpon,  dominating  large 
areas  with  its  orange-colored  thallus.  It  is  often  accompanied 
by  the  cinnamon-brown  Lecidea  fuscocinerea.  Further  investiga- 
tion will  probably  show  these  to  be  dominants  of  a  distinct  as- 
socies. 

Often  large  areas  of  vertical  cliffs  of  basalt  appear  as  if  painted 
lemon-color  because  of  the  presence  of  the  crustose  Acarospora 
chlorophana. 

Crustose  lichens  not  only  exert  an  influence  at  the  contact  of 
thallus  and  rock,  but  the  corroding  effect  of  carbon  dioxide  and 
other  secretions  extends  beyond  the  thallus  margins  during  moist 
weather.  This  permits  slow  extension  of  the  thalli  or  furnishes 
the  starting  place  for  new  ones.  Thus  lichens  corrode  and  de- 
compose the  rock  and  by  mixing  its  particles  with  their  own  re- 
mains give  opportunity  for  the  growth  of  other  vegetation.  Cen- 
ters of  crustose  thalli  break  up  and  folious  lichens  get  in.  Espe- 
cially on  the  more  weathered  rocks  and  in  slightly  less  exposed 
situations  a  number  of  foliose  lichens  replace  crustose  forms. 


Southeastern  Washington  and  Adjacent  Idaho.  65 

About  the  foliaceous  species,  water  not  only  has  a  better  chance 
to  collect  and  be  absorbed  but  evaporation  is  also  less  rapid.  In- 
deed, it  is  probable  that  the  change  from  crustose  to  f oliose  lichens 
is  as  great  a  change  of  habitat  as  happens  anywhere  in  the  sere, 
although  too  minute  in  extent  to  be  impressive. 

Gyrophora-Parmelia  Associes 

This  community  is  in  general  less  marked  than  the  preceding 
and  is  characterized  by  the  following  f  oliose  forms : 

Dermatocarpon  miniatum  Parmelia  conspersa 

Gyrophora  phaca  Parmelia  pubescens 

Lecanora  rubina 

Gyrophora  phaca  may  easily  be  found  invading  the  areas  of 
the  preceding  crustose  forms  and  because  of  its  growth-form 
actually  causing  them  to  disappear  on  account  of  decreased  light. 
Thus  it  comes  to  dominate  areas  of  greater  or  lesser  extent. 
Parmelia  conspersa  takes  possession  of  new  areas  in  a  similar 
manner.  Dermatocarpon  miniatum  is  characteristically  found  in 
situations  where  water  seeps  out  of  the  rock  ledges  during  a  part 
of  the  year.  . 

As  soon  as  soil  and  humus  begin  to  accumulate  in  the  crevices 
and  larger  pores  of  the  rock,  the  more  xerophilous  mosses  begin 
to  appear.  The  pores  in  the  basalt  vary  from  those  microscopic 
in  size  to  those  several  inches  or  even  feet  in  diameter.  On  a 
single  rock  one  may  come  across  an  infinite  variety  of  stages  from 
the  dry  exposed  top  of  the  rock  with  its  crustose  lichens  to  the 
creviced  or  roughened  lower  portions  where  foliose  forms  are 
mixed  with  mosses,  grasses,  and  other  flowering  plants. 

Grimmia-Tortula  Associes 

The  moss  of  most  common  occurrence  on  the  rocks  and  the  one 
which  is  able  to  live  in  the  most  xerophytic  situations  is  the  black 
moss,  Grimmia  montana.  This  moss,  with  its  minute  rhizoids  and 
power  of  withstanding  desiccation,  quickly  follows  the  lichen  stage 
and  even  precedes  several  species  of  the  foliose  lichens  in  point 

65 


66  A  Study  of  the  Vegetation  of 

of  succession.  Starting  from  the  vantage  ground  of  a  crack  or 
crevice,  the  small  tufts  collect  wind-blown  soil  and  lichen  remains 
about  them  and  building  upon  this  substratum  increase  their 
area.  Well-worn  rocks  are  frequently  covered  with  the  black 
mats  of  the  Grimmia  consocies. 

Less  xerophytic  but  far  more  abundant  is  Tortula  rurolis. 
Growing  in  places  less  dry  than  those  occupied  by  Grimmia,  it 
surrounds  the  base  of  rocky  outcrops  and  occurs  on  thin  stony 
soil  where  its  soft  cushiony  mats  may  cover  areas  of  many  square 
meters.  While  Tortula  is  very  abundant  on  basaltic  ledges  it  is 
sometimes  partly  or  wholly  replaced,  especially  about  quartzite 
rocks,  by  species  of  Polytrichum,  especially  P.  piliferum  and  P. 
juniperinum. 

In  other  situations,  and  especially  on  canyon  walls  with  north 
and  northeast  exposure  other  mosses  are  abundant,  often  covering 
large  areas  of  sheer  rock  surface  or  growing  luxuriantly  over  the 
thin  stony  soil.  The  following  lists  include  the  most  important 
of  these  together  with  a  number  of  lichens  which  usually  occur 
with  the  mosses.  Some  of  these  lichens  are  less  xerophytic  than 
the  foliaceous  forms  already  mentioned.  Indeed,  they  are  the 
most  exacting  members  of  the  foliose  lichen  community. 

Brachythecium  albicans  Ceratodon  purpureus 

Brachythecium  erythrorrhizon  Encalypta  ciliata 

Camptothecium  aeneum  Grimmia  apocarpa 

Camptothecium  lutescens  Mnium  affine 

Cladonia  pyxidata  Ochrolechia  upsaliensis 

Diploschistes  scruposus  Peltigera  canina 

Poa-Polygonum  Associes 

In  the  thin  soil  between  the  fragments  of  broken  rock,  an  area 
over  which  Tortula  ruralis  and  other  mosses  for  a  time  have 
control,  bunches  of  June  grass  and  plants  of  Polygonum  majus 
and  Plantago  purshii  begin  to  appear  (Fig.  18).  Changes  of 
light  and  root  competition  react  unfavorably  upon  the  mosses, 
while  shallow-rooted  plants  are  well  adapted  to  dominate  just 

66 


Southeastern  Washington  and  Adjacent  Idaho.  67 

such  areas.  The  broken  rock  fragments  not  only  aid  in  the 
percolation  of  water  and  prevent  run-off,  but  also  tend  to  reduce 
evaporation. 

The  xerophytic  character  of  Poa  sandbergii  has  been  discussed. 
Polygonum  majus  with  its  wiry  stems  and  diminutive  leaves 
answers  well  ecologically  for  a  grass.  Likewise,  the  linear-leaved, 
spiked,  densely  hairy  Plantago  may  be  so  considered. 

Polygonum  majus  must  be  a  plant  of  very  low  water  require- 
ment for,  in  spite  of  its  shallow  roots,  it  blossoms  and  appears 
to  thrive  throughout  the  summer  and  fall  in  these  stony  soils.  It 
is  especially  noticeable  among  the  rocks  when  most  other  plants 
are  dried  out,  and  its  abundance  makes  it  showy  notwithstanding 
its  tiny  flowers.  I  have  counted  more  than  1,000  individual  plants 
from  2-8  inches  high  in  a  single  square  meter.  In  deeper  soils 
of  talus  slopes  it  becomes  a  bushy  plant,  sometimes  more  than  a 
foot  in  height. 

In  the  scab-lands  especially,  Plantago  purshii  characterizes 
large  areas  with  its  leaden  color. 

The  following  plant  lists  include  those  especially  characteristic 
of  this  community : 

. 
Composition  of  the  Poa-Polygonum  Associes 

Dominant  Species  (Consocies) 

Plantago  purshii  Polygonum  majus 

Poa  sandbergii 

Principal  Species 

Antennaria  dimorpha  Eriogonum  heracleoides 

Antennaria  luzuloides  Epilobium  paniculatum 

Clarkia  pulchella  Festuca  pacifica 

Cogswellia  grayi  Madia  exigua 

Cogswellia  gormani  Madia  glomerata 

Secondary  Species 

Agoseris  heterophylla  Allium  acuminafum 

Ago  sens  grandiflora  Alsine  nit  ens 


68  A  Study  of  the  Vegetation  of 

Alyssum  alyssoides  Festuca  megalura 

Arabis  sparsiflora  Platyspermum  scapigerum 

Arabis  holboellii  Ranunculus  glaberrimus 

Athysanus  pusillus  Sedum  douglasii 

Bromus  brizaeformis  Selaginella  wallacei 

Cogswellia  macrocarpa  Tellima  tenella 

Draba  verna  Tellima  parviflora 

Eriogonum  niveum  Thysanocarpus  curvipes 
Eriogonum  compositum 

A  number  of  the  above  species  form  more  or  less  well  de- 
veloped socies.  Cogswellia  gormani,  one  of  the  earliest  of  pre- 
vernal  plants,  though  inconspicuous  as  an  individual,  grows  in 
such  great  numbers  on  the  thin  soils  as  to  become  quite  promi- 
nent in  early  spring.  When  500-800  of  these  plants  occur  in  a 
square  meter,  as  is  often  the  case,  with  perhaps  a  third  of  them 
in  blossom,  they  indeed  make  the  landscape  appear  as  if  covered 
with  "  salt-and-pepper." 

Cogswellia  grayi  is  much  more  important  than  C.  gormani.  It 
covers  large  areas  of  rim-rock  almost  to  the  exclusion  of  other 
species.  Its  large  umbels  of  yellow  flowers  make  it  very  con- 
spicuous. 

Moist  places  on  the  thin  soils  are  dominated  for  a  time  in  early 
spring  by  great  patches  of  Ranunculus  glaberrimus,  a  small  plant 
but  one  with  large  and  showy  flowers. 

The  Poa-Polygonum  associes  gives  way  to  the  community 
dominated  by  Agropyron.  The  chief  cause  for  the  transition  is 
the  accumulation  of  soil  and  the  presence  of  rock  crevices  of 
sufficient  depth  and  width  to  furnish  soil  and  water  for  the  deep- 
rooted  bunch-grass.  The  early  stage  of  the  Agropyron  con- 
sociation, already  described,  well  illustrates  this  change.  Often 
however,  in  the  rim-rock  throughout  the  less  arid  region,  the 
transition  is  more  abrupt.  Belt  transects  only  a  few  meters  long 
often  show  zones  of  vegetation  dominated  by  the  characteristic 
species  of  the  Poa-Polygnum,  Agropyron,  and  Festuca  com- 
munities respectively.  These  zones  extend  in  a  parallel  manner 
along  the  upper  edge  of  rocky  outcrops.  Below  the  transition 

-  68 


Southeastern  Washington  and  Adjacent  Idaho.  69 

may  be  even  more  abrupt,  a  linear  distance  of  one  or  two  meters 
giving  the  necessary  differences  in  soil  depth.  Consequently  the 
zones  are  narrower,  but  no  less  distinct. 

The  uneven  disintegration  of  canyon  walls  and  scab-land  and 
rocky  butte  ledges  and  the  differences  they  offer  in  slope  and 
exposure  and  in  depth  and  moisture  of  soils  furnish  so  many 
habitat  conditions  that  perhaps  two-thirds  of  the  total  flora  find 
here  more  or  less  congenial  homes.  In  the  crevices  of  a  lichen- 
covered  rock  and  separated  only  a  few  inches  from  the  lowly 
inhabitants  of  the  former  may  thrive  a  shrubby  member  of  a  far 
more  advanced  community.  An  analysis  of  the  habitat  shows 
each  is  growing  in  its  proper  place,  the  crustose  lichen  on  the  bare 
rock,  the  shrub  in  a  small  area  of  rich,  well  moistened  soil. 

Striking  differences  are  offered  by  habitats  on  sheltered  and 
protected  slopes.  Near  Pullman,  during  the  summer  of  1913, 
a  station  was  maintained  on  a  south  slope  in  the  Agropyron 
community  and  a  second  in  a  rather  open  growth  of  low  shrubs  on 
the  opposite  slope  about  half-way  between  the  rock  ledge  and  the 
flood-plain  thicket.  Not  only  was  the  evaporating  power  of  the 
air  found  to  be  twice  as  great  in  the  former  situation,  but  the  soil 
moisture  was  only  about  half  as  great  throughout  the  growing 
season.  Temperature  differences  were  also  striking.  The  soil 
between  the  bunches  of  Agropyron  frequently  gave  noonday 
temperatures  of  90°  to  100°  F.,  as  compared  with  70°  F.  at  the 
opposite  station. 

These  illustrations  of  diverse  habitat  conditions  will  make  plain 
the  fact  that  in  addition  to  the  plants  already  mentioned  as 
belonging  to  the  Agropyron  or  Poa-Polygonum  communities, 
many  others  occur. 

Characteristic  shrubs  and  lianas  found  either  as  crevice  plants 
on  rocky  talus  slopes  or  forming  thickets  about  springy  places 
are  enumerated  in  the  following  lists :  the  numerals  indicate  their 
relative  importance.  In  the  drier  regions  the  shrubs  are  notably 
fewer. 

Amelanchier  florida  2  Berberls  repens  I 

Amelanchier  cusickii  I  Clematis  ligusticifolia  2 


70  A  Study  of  the  Vegetation  of 

Crataegus  columbiana  2  Ribes  cereum  I 

Opulaster  pauciflorus  2  Ribes  cognatum  2 

Philadelphus  lewisii  I  Rosa  nutkana  i 

Prunus  demissa  I  Rosa  pis  o  car  pa  2 

Rhus  glabra  2  Sambucus  glauca  2 

Rhus  toxicodendron  2  Spiraea  corymbosa  2 

Ribes  aureum  2  Symphoricarpos  racemosus   I 

In  springy  places  among  the  rocks,  which  are  often  surrounded 
by  thickets,  the  following  herbs  are  especially  plentiful : 

Alsine  media  Hydrophyllum  capita-turn 

Cerastium  vulgatum  Mentha  canadensis  borealis 

Claytonia  parviflora  Mimulus  langsdorfii 

Equisetum  arvense  Saxifraga  columbiana 
Equisetum  hyemale  robustum        Scutellaria  angustifolia 

Galium  aparine  Vagnera  sessilifolia 

Galium  asperrimum  Veronica  americana 

Among  the  most  typical  crevice  plants  other  than  those  previ- 
ously enumerated  may  be  mentioned  two  ferns,  Cheilanthes  gracil- 
lima  and  Woodsia  oregana.  The  former  is  especially  character- 
istic of  stony  outcrops  on  the  buttes  and  mountains.  Heuchera 
glabella  should  also  be  mentioned  here. 

Other  species  peculiar  to  thin  soils  of  rocky  ledges  are: 

Amsinckia  intermedia  Phacelia  he'terophylla 

Arabis  holboellii  Sisymbrium  altissimum 

Crepis  gracilis  Thalesia  unifiora 

Gilia  aggregata  Valerianella  macrocera 

The  kaleidoscopic  character  of  scab-land  vegetation  may  well 
be  anticipated  by  a  glance  at  Fig.  39. 

In  the  thin  soil  surrounding  lichen-  or  moss-covered  basalt  may 
be  found  herbaceous  plants  characteristic  of  the  Poa-Polygonum 
community.  Or  these  may  alternate  with  the  shrubby  growth 
of  scab-land  sage.  In  the  crevices  of  the  rocks  may  be  seen 

70 


Southeastern  Washington  and  Adjacent  Idaho.  71 

dwarfed  bunches  of  Agropyron  which  is  better  developed  on  the 
talus  slope  below.  This  gives  way  in  the  deeper  soils  of  the 
depressions  or  on  protected  slopes  to  various  lupines,  species  of 
Poa,  Balsamorhiza,  Hieracium,  Gaillardia,  and  other  species.  The 
depressions,  if  alkaline,  may  be  clothed  with  dense  growths  of 
Distichlis  spicata,  Spartina  gracilis,  or  Poa  brachyglossa  and  these 
surrounded  by  a  more  or  less  distinct  zone  of  Elymus  condensatus. 
The  vegetational  differences  often  occur  in  areas  so  local  as 
to  be  seen  at  a  single  glance.  Alternating  with  a  talus  slope  of 
lichen-covered  basaltic  blocks  and  only  a  few  feet  away,  may  be 
seen  other  slopes  which  at  a  little  distance  appear  well  clothed 
with  herbaceous  vegetation.  Such  are  the  interesting  situations 
offered  by  the  rocky  soils  of  canyons  and  scab-lands. 

DESERT  SCRUB  FORMATION 

In  the  region  under  investigation  the  above  formation  is  repre- 
sented only  in  the  extreme  western  part.  This  formation  oc- 
cupies much  of  the  Columbia  Basin,  extending  eastward  to  an 
altitude  of  about  1,200-1,300  feet,  and  on  southerly  slopes  much 
higher.  Excepting  such  species  as  are  confined  to  the  moist 
ground  along  perennial  streams,  the  great  majority  of  plants  are 
either  shrubs  or  thick-rooted  perennial  herbs  or  short-lived 
annuals.  The  most  conspicuous  and  ecologically  important  plant 
is  Artemisia  tridentata.  Other  dominant  species  are  the  rabbit 
brush,  Chrysothamnus  nauseosus,  C.  viscidiflorus,  the  scab-land 
sage,  Artemisia  rigidia}  the  antelope  brush,  locally  known  as  the 
black  sage,  Kunzia  tridentata,  and,  in  alkaline  situations,  the 
greasewood,  Sarcobatus  vermicula\tus. 

The  life  conditions  in  this  region  are  strikingly  more  severe 
than  in  the  region  of  the  high  prairies  eastward.  During  the 
summer  of  1914,  Mr.  James  G.  Dickson,  my  .one-time  student, 
made  determinations  of  water  content,  evaporating  power  of  the 
air,  and  soil  temperature  for  a  period  extending  from  July  5  to 
August  15,  at  Moxee,  Washington,  in  the  heart  of  this  formation. 
He  found  that  the  average  daily  evaporation  throughout  the 
period  from  standard  atmometers  was  51  c.c.,  while  during  several 
days  in  August  it  reached  74  c.c.  The  soil  moisture  at  6  and  12 


72  A  Study  of  the  Vegetation  of 

inches  respectively,  never  exceeded  2.8  per  cent.,  while  that  at  a 
depth  of  2  and  3  feet  was  only  slightly  higher.  Conversely,  the 
soil  temperature  at  3  inches  ranged  from  77°  F.  to  over  112°  F. 
Even  at  12  inches  the  temperature  was  usually  above  78°  F. 

The  Artemisia- A  triples  association  is  represented  in  this  region 
by  the  Artemisia  consociation. 

The  Artemisia  Consociation 

This  consociation,  dominated  by  Artemisia  rigida,  is  a  very 
characteristic  type  of  vegetation  over  large  areas  of  scab-lands. 
The  scab-lands,  as  elsewhere  indicated,  are  areas  of  basalt,  prob- 
ably the  flood-plains  of  former  streams,  in  part,  thinly  covered 
with  soil.  These  extend  as  long  tongues  over  the  branching  sys- 
tem of  river  tributaries  between  the  hilly  divides.  While  many 
of  these  flats  in  this  region  are  dominated  by  communities  of 
Agropyron  or  Poa-Polygonum,  still  large  areas  are  characterized 
by  the  scab-land  sage.  This  perennial,  low,  scrubby  growth  is 
well  adapted  to  the  driest  situations  on  the  thin,  rocky  soil  (Fig. 
1 6).  Many  species  typical  of  the  above  mentioned  communities 
occur  associated  with  the  sage,  as  might  be  expected  in  this  zone 
of  transition.  Plants  characteristic  of  the  desert  scrub  forma- 
tion occurring  with  the  sage  are  Chrysothamnus  nauxeosus  in- 
cluding the  variety  graveolens,  C.  viscidiflorws,  and  Tetradymia 
canescens.  It  has  already  been  pointed  out  that  some  of  these 
play  an  important  role  in  the  Agropyron  consociation. 

In  the  Snake  River  Canyon  beautiful  examples  of  the  abrupt 
transition  from  the  sage  to  the  Agropyron  community  are  abun- 
dant. Rocky,  exposed  slopes  reveal  the  former,  while  sheltered 
slopes  only  a  few  meters  distant  show  a  well  developed  Agro- 
pyron community. 

In  passing  from  the  prairie  into  the  scab-land  the  change  in 
animal  population  is  no  less  striking  than  that  of  the  vegetation. 
In  the  drier  region  the  Townsend  squirrel,  Citellus  townsendi, 
replaces  the  larger  Columbian  squirrel,  C.  columbianus,  so  plenti- 
ful eastward.  Likewise  the  presence  of  the  burrowing  owl  and 
rattlesnake  is  characteristic. 

72 


Southeastern  Washington  and  Adjacent  Idaho.  73 

The  Sarcobatus  Consocies 

Communities  of  the  greasewood,  Sarcobatus  vermiculaius, 
occur  in  alkaline  soils  of  the  flood  plains  or  depressions  in  the 
scab-lands.  This  scrubby  growth,  with  its  pale  branches  and 
fleshy  leaves,  stands  out  in  distinct  contrast  to  surrounding  vege- 
tation. The  consocies  is  represented  only  locally  and  careful 
study  of  it  was  not  made. 

THE  PACIFIC  COAST  FOREST  FORMATION 
The  coniferous  woodland  occurs  in  the  eastern  part  of  the  re- 
gion and  chiefly  in  Idaho.  While  the  forests  in  the  main  grow 
on  the  soils  produced  by  the  weathering  of  old  crystalline  rocks, 
it  is  not  uncommon  in  certain  parts  of  the  region  to  find  under- 
lying rocks  of  basalt.  Likewise,  the  sheltered  slopes  of  isolated 
quartzite  buttes  may  be  clothed  with  trees,  or  woodland  may  ex- 
tend as  tongues  along  the  deeper  canyons  far  into  the  prairie. 

There  exists  a  close  relation  between  the  development  of  the 
physiography  of  a  region  and  the  life  history  of  its  forest  com- 
munities. This  is  nowhere  better  shown  than  in  semi-arid  cli- 
mates where  a  slight  change  in  elevation  may  so  modify  the  pre- 
cipitation and  other  life  conditions  as  to  turn  the  balance  slightly 
or  wholly  in  favor  of  a  tree  form  of  vegetation. 

A  study  of  the  chemical  composition  of  the  soils  of  basaltic 
origin  as  compared  with  those  originating  from  quartzite,  granite, 
and  other  crystallic  rocks,  shows  that  they  are  not  greatly  dissimi- 
lar (Table  III).  I  am  convinced  that  it  is  not  the  chemical  com- 
position of  the  soils  of  this  region  but  rather  their  physical  char- 
acters that  determine  the  type  of  vegetation  which  they  support. 
Of  course  the  controlling  factor  of  the  physical  composition 
is,  in  this  region  of  dry  summers,  their  ability  to  hold  water,  pro- 
vided always  that  sufficient  humus  is  present  to  furnish  the  neces- 
sary nitrates.  Not  only  do  these  forest  soils  have  a  higher  water 
holding  capacity  than  those  of  the  basaltic  prairies,  as  has  already 
been  shown,  but  this  property  increases,  due  to  increased  humus 
content,  proportionally  as  the  succession  advances  toward  the 
climax  stage.  That  coniferous  forests  will  grow  upon  the  basaltic 
soils  is  evidenced  by  their  presence  over  considerable  areas  in  the 

73 


74  A  Study  of  the  Vegetation  of 

upper  Palouse  Valley,  but  the  best  example  is  to  be  found  in  the 
woodland  growth  of  that  high  upfold  of  basalt  in  southeastern 
Washington  known  as  the  Blue  Mountains.  Under  the  present 
climatic  conditions,  the  prairies  appear  to  be  a  subclimax  forma- 
tion. 

The  higher  elevation  of  these  forest-clad  foothills  and  moun- 
tains is  sufficient  to  considerably  increase  the  precipitation.  The 
prevailing  southwest  winds  sweeping  across  the  many  miles  of 
open  prairie  and  desert  of  northern  Oregon  and  south  central 
Washington,  but  gradually  ascending,  here  lose  much  of  their  mois- 
ture. It  is  not  unusual  to  observe  on  a  morning  in  autumn  or 
late  spring  the  surrounding  mountains  covered  with  snow  while 
no  moisture  has  fallen  upon  the  lower  hills.  Sometimes  even  iso- 
lated buttes  only  700-1,000  feet  higher  than  the  lava  plateau  are 
snow  clad  and  stand  out  in  bold  relief  in  contrast  to  the  surround- 
ing country. 

A  rain  gauge  of  the  government  pattern  placed  with  Mr.  J.  B. 
Kissinger  4  miles  northeast  of  Viola,  Idaho,  showed,  during  the 
years  1912-1914,  an  annual  increase  over  the  rainfall  at  Pullman 
during  the  same  period  of  3  and  4.5  inches  respectively.  A  simi- 
lar gauge  placed  with  Mr.  Stratton  on  Cedar  Mountain  and  at 
an  elevation  of  about  4,000  feet  gave  4  inches  greater  precipita- 
tion during  the  months  of  July  and  August,  1914,  than  was  re- 
corded at  the  base  station.  Not  infrequently,  I  have  witnessed 
rather  heavy  summer  showers  in  the  mountains  while  no  rain  fell 
upon  the  plateau  1,500  feet  below. 

Not  only  does  the  change  in  altitude  affect  the  amount  of  pre- 
cipitation, but  it  also  shortens  the  growing  season.  Snow  lies  on 
the  ground  until  late  in  May  or  indeed  on  the  more  protected 
slopes  even  until  June.  Thus,  the  season  of  drought  is  consider- 
ably shortened.  Likewise,  the  cool  nights  lessen  the  evaporating 
power  of  the  air. 

The  forests  of  the  region  make  up  a  part  of  the  Pacific  Coast 
forest  formation.  This  formation  is  represented  by  the  Thuja- 
Tsuga  association.  A  single  consociation,  dominated  by  Thuja 
plicata,  forms  the  climax  community.  Tsuga  heterophylla,  an 

74 


Southeastern  Washington  and  Adjacent  Idaho.  75 

important  member  of  the  climax  communities  elsewhere,  is  not 
represented  in  the  area  under  consideration. 

Symphoricarpos-Opulaster  Associes 

A  shrub  community  usually  occupies  the  transition  zone  be- 
tween prairie  and  forest  or  at  least  is  intimately  associated  with 
the  earlier  stages  of  development  of  the  latter.  I  have  already 
mentioned  that  on  the  most  mesophytic  hillsides  a  more  or  less 
well  developed  scrubby  mictium  may  compete  with  the  grasses. 
These  shrubs  are  even  better  developed  on  the  protected  slopes 
of  the  canyons,  where  seepage  from  the  rocks  may  form  a  very 
congenial  habitat,  and  where,  indeed,  they  often  entirely  replace 
the  prairie.  Likewise,  the  sheltered  sides  of  the  lower  buttes 
and  the  more  exposed  slopes  of  those  of  greater  elvation  may  be 
covered  with  a  rather  dense  chaparral.  The  presence  of  such  a 
shrubby  growth  indicates  increased  soil  moisture.  This  at  first 
may  be  due  to  slight  unevenness  in  the  topography  such  as  a  ridge 
over  which  snow  may  be  blown  and  accumulate  in  sufficient 
quantity  to  furnish  considerable  additional  moisture,  or,  it  may  be 
due  to  biotic  factors  such  as  the  loosening  of  the  soil  by  squirrels 
and  other  burrowing  animals.  The  water  holding  capacity  of 
such  worked-over  areas  is  considerably  increased  and  results  in 
an  immediate  dominance  of  various  shrubs,  especially  roses,  Sym- 
phoricarpos  or  Spiraea,  which  show  a  much  poorer  development 
in  the  drier,  compact  soils.  The  shrubs  once  present  tend  to 
make  conditions  more  mesophytic,  a  phase  which  constitutes  their 
most  important  role  in  succession.  Not  only  do  their  fallen 
leaves  but  also  their  decaying  roots  and  rhizomes  add  considerable 
humus  to  the  soil,  while  their  shade  lowers  the  rate  of  evapora- 
tion from  the  soil  and  at  the  same  time  prevents  the  too  rapid 
oxidation  of  the  decaying  organic  matter.  Such  enriched  soil 
forms  an  excellent  seed  bed  for  species  of  xerophytic  trees  which 
may  invade  the  sodded  prairies  only  with  difficulty.  Thus  in  the 
normal  succession  the  shrubs  may  prepare  the  way  for  tree 
growth.  The  trees  in  their  turn,  because  of  their  shade,  espe- 
cially if  they  are  in  dense  stands,  cause  the  shrubs  to  disappear. 

The  Symphoricarpos-Rosa  Mictium. — The   members   of   this 

75 


76  A  Study  of  the  Vegetation  of 

community  although  present  generally  throughout  the  less  xero- 
phytic  portion  of  the  prairie  region  seldom  come  into  dominance 
except  on  moist  sheltered  slopes  or  ravines.  In  such  situations, 
dense  tangles  of  shrubby  growth  consisting  of  the  following 
species  may  occur: 

Rosa  nutkana  Spiraea  corymbosa 

Rosa  gymnocarpa  V actinium  caespitosum 

Symphoricarpos  racemosus  Prunus  demissa 

Here,  as  along  sheltered  canyon  slopes,  they  may  dominate  local 
areas  almost  to  the  exclusion  of  grasses  and  herbaceous  plants. 
They  are  frequently  accompanied,  especially  in  the  latter  situa- 
tions, by  dwarfed  specimens  of  Crataegus  brevispina,  Amelan- 
chier  spp.,  or  Populus  tremuloides.  Where  pines  occur  the  pre- 
ceding trees  and  shrubs  are  invariably  accompanied  by  Opulaster 
pauciflorus,  the  latter  usually  becoming  the  dominant  shrub. 

The  roses  are  especially  conspicuous  in  May,  when  their  large 
showy  blossoms  fill  the  air  with  a  delicate  perfume.  Spiraea  is 
always  less  conspicuous,  while  Symphoricarpos  is  much  more 
noticeable  in  the  fall  when  it  is  covered  with  its  large  white  fruits, 
than  throughout  its  flowering  period.  Vaccinium  caespitosum 
often  covers  large  areas  and  while  its  reddish  leaves  may  add  tone 
to  the  vernal  aspect,  later,  because  of  its  low  stature,  it  is  more  or 
less  hidden  by  other  vegetation. 

Opulaster  Consocies. — As  already  indicated  Opulaster  pauci- 
florus is  the  shrub  par  excellence  of  the  scrub  community.  It 
often  covers  large  areas  in  almost  pure  growth  'especially  in  the 
deeper  canyons  and  on  the  outlying  buttes.  Its  well  developed  rhi- 
zones  enable  it  to  invade  the  grass  land  which  soon  gives  way  be- 
cause of  the  dense  shade,  if  the  shrubs  are  well  developed.  In 
most  situations,  the  balance  between  chaparral  and  prairie  is  so 
nicely  adjusted  that  for  a  long  time  the  shrubs  occupy  places  in 
swales,  ravines,  or  other  irregularities  of  the  surface,  while 
tongues  of  grass  land  extend  down  on  the  slightly  higher  eleva- 
tions (Fig.  23).  Among  the  last  herbaceous  plants  to  give  way 
are  those  of  the  more  mesophytic  type  such  as  Geranium,  Dry- 


Southeastern  Washington  and  Adjacent  Idaho.  77 

mocallis,  and  Sidalcea,  but  not  infrequently  Opulaster  grows  in 
such  situations  as  to  replace  the  more  xerophytic  grasses  and 
Balsamorhiza. 

Chaparral  that  is  so  dense  as  to  almost  exclude  other  vegetation 
is  characterized  in  early  spring  and  before  the  leaves  appear  by  a 
layer  society  of  Erythronium  grandiflorum.  These  lilies  are 
often  so  numerous  as  to  give  the  appearance  of  a  yellow  carpet 
'under  the  shrubs.  In  less  shaded  areas  Ranunculus  glaberrimus 
and  Olsynium  grandiflorum  are  plentiful.  The  Opulaster  con- 
socies  is  very  conspicuous  in  May,  when  its  countless  white  blos- 
soms give  a  distinct  tone  to  the  landscape.  Likewise,  in  late 
August  and  September  the  reddish-tinted  drying  leaves  form  a 
pleasing  variety  to  the  monotonous  brown  of  dry  vegetation. 

While  Opulaster  frequently  characterizes  considerable  areas 
alone,  it  is  not  infrequently  associated  with  the  buckbrush, 
Ceanothus  sanguineus.  Indeed,  the  latter  shrub  may  sometimes 
become  so  abundant  as  to  make  up  half  of  the  mictium.  The 
buckbrush  because  of  its  oily  seeds,  is  a  very  important  and  fat- 
tening food  for  sheep  on  the  summer  range.  Numerous  other 
shrubs,  such  as  Holodiscus  discolor,  Prunus  emarginata,  and 
species  of  Ribes  are  less  important  components  of  this  consocies. 

Prunus  Consocies. — Local  areas  on  the  buttes  are  often  charac- 
terized by  growths  of  Prunus  emarginata.  These  vary  from  a 
rather  open  growth  of  stunted  shrubs  only  three  feet  high  to 
dense  copses  in  which  the  cherry  takes  on  the  stature  of  a  small 
tree.  The  characteristic  occurrence  of  this  community  in  dry 
open  places  is  of  considerable  ecological  significance.  I  have  not 
infrequently  found  invading  pines  extending  their  territory  from 
sheltered  slopes  into  the  drier  areas  under  cover  of  these  shrubs. 
Frequently  the  pines  may  be  overtopping  the  cherries  and  indeed 
beginning  to  replace  them,  yet  a  count  of  annual  rings  usually 
shows  that  the  latter  were  the  pioneer  woody  plants. 

Ceanothus  Consocies. — On  the  exposed  slopes  of  Cedar  Moun- 
tain and  adjacent  buttes,  but  seldom  found  elsewhere  in  the  re- 
gion, the  sticky  laurel,  Ceanothus  velutinus,  often  dominates. 
This  evergreen,  semi-procumbent  shrub,  while  seldom  reaching  a 
height  of  over  4—6  feet,  has  numerous  long  branches  which  spread 

77 


7$  A  Study  of  the  Vegetation  of 

in  all  directions  so  that  a  single  plant  may  cover  an  area  'of  sev- 
eral square  meters.  It  is  frequently  so  abundant  as  to  form  a 
dense  tangle  very  difficult  to  penetrate.  Other  common  shrubs 
associating  with  it  are  Ceanothus  sanguineus,  Pachistima  myr- 
sinitis,  Salix  scouleriana,  Holodiscus  discolor,  and  Spiraea  corym- 
bosa.  On  these  steep,  gravelly  slopes  the  role  of  the  shrubs  in 
catching  surface  washed  materials  including  coniferous  seeds 
which  are  frequently  buried  under  the  debris,  and  in  shading  the1 
soil  against  excessive  evaporation,  is  an  important  one  in  the 
establishment  of  the  tree  stage  in  succession.  Of  the  forest  trees, 
Pinids  ponderosa  and  Pdeiidotsuga  mucronata  are  most  likely 
to  be  found  in  such  situations. 

The  Pinus-Pseudotsuga  Associes 

Although  much  of  the  forest  in  this  region  has  been  cut  over 
and  still  larger  areas  swept  by  forest  fires,  yet  large  tracts  repre- 
senting all  the  consocies  and  mictia  of  the  region  are  still  found 
in  their  primeval  condition.  This  is  due  to  the  rough  topography 
which  makes  them  'inaccessible  to  the  lumberman,  while  certain 
areas  have  been  set  aside  by  the  federal  government  as  mineral 
lands. 

The  above  associes  represents  types  of  forest  which  occupy  the 
drier  mountain  slopes  and  are  the  transition  stage  from  the  grass 
land  and  shrub  to  the  more  mesophytic  forest  communities. 
Here  are  included  the  yellow  pine  and  the  Douglas  fir  consocies 
and  a  pine-fir  mictium.  The  former  is  the  earliest  in  point  of 
succession  and  will  be  considered  first. 

Pinus  Consocies. — Of  all  the  forest  trees  of  the  region  the 
yellow  pine  is  best  fitted  for  the  pioneer  work  of  foresting  prairie, 
chaparral,  or  rocky  areas.  It  overcomes  xerophytic  conditions  in 
part  by  striking  its  root-system  deeply  and  spreading  it  widely, 
thus  laying  hold  upon  large  areas  of  soil.  Rooted  in  rock  crev- 
ices it  may  make  a  height  growth  of  only  a  fraction  of  an  inch  a 
year  and  at  the  age  of  40  or  50  years  be  only  a  few  feet  high,  yet 
such  examples  bear  witness  to  its  wonderful  powers  of  resisting 
adverse  conditions. 

The  difficulties  of  pines  in  invading  grass  lands  should  be  recog- 

78 


Southeastern  Washington  and  Adjacent  Idaho.  79 

nized.  Many  of  the  seeds  which  are  overlooked  by  rodent  popu- 
lations never  germinate.  Of  those  that  do  germinate  many  dry 
out  before  they  have  become  well  established.  Other  seeds  are 
prevented  from  reaching  the  soil  because  of  the  sod.  However, 
under  a  combination  of  favorable  conditions  a  few  seedlings  be- 
come fairly  established.  Surface  wash  may  lodge  the  seeds 
against  a  rock  or  bush  or  other  obstacle  and  at  the  same  time 
cover  them  with  soil.  Opportune  showers  may  so  favor  their 
growth  that  they  become  well  established.  Having  gained  a  per- 
manent foothold  they  may  reach  maturity.  These  pioneer  trees 
establish  a.  more  congenial  habitat  for  their  offspring.  The  fallen 
needles  and  branches  catch  more  surface  water  and  debris,  and 
decaying,  aid  the  grasses  in  increasing  the  humus  content  and 
consequent  water  holding  capacity  of  the  soil.  Likewise,  shading 
prevents  the  rapid  oxidation  of  humus  and  at  the  'same  time 
lowers  the  evaporating  power  of  the  air.  It  is  not  unusual  to 
find  parent  trees  in  prairie  openings  establishing  about  themselves 
just  such  areas  of  ecesis.  In  this  way  forests  may  replace 
prairies. 

The  invasion  of  pines  into  chaparral  is  accomplished  with  less 
difficulty,  especially  if  the  latter  is  of  not  too  dense  a  growth. 
The  shrubs  not  only  modify  the  edaphic  condition  in  a  manner 
already  indicated  but  also  the  aerial  plant  parts  are  greatly  shel- 
tered, especially  from  drying  winds.  I  have  noted  scores  of  situa- 
tions where  shrubs  were  advancing  up  butte  slopes  into  the  prairie, 
while  numerous  pine  trees  of  all  sizes  and  ages  had  established 
themselves  in  the  chaparral.  However,  the  chaparral  is  often 
so  dense  as  to  prevent  the  establishment  of  the  pines.  This 
happens  when  the  light  under  the  shrubs  falls  to  an  intensity  of 
0.15.  But  usually,  even  in  such  situations,  there  are  open  places 
in  which  forest  growth  may  occur  provided  tree  seeds  are  present. 

It  is  probable  in  this  semi-arid  region  that  during  the  more 
favorable  years  of  a  climatic  cycle  the  forest  trees  are  able  to 
gain  a  foothold  in  situations  where  growth  conditions  would  be 
too  severe  ordinarily.  An  investigation  along  this  line  would 
probably  throw  considerable  light  upon  the  puzzling  problem  of 
an  isolated  stretch  of  yellow  pine  in  the  canyon  of  Union  Flat 

79 


8o  A  Study  of  the  Vegetation  of 

Creek,  at  a  distance  of  12  miles  from  any  contiguous  body  of 
timber.  However,  this  is  a  phase  of  the  problem  which  I  found 
little  time  to  study. 

The  yellow  pine  consoci-es  forms  the  transition  zone  from 
prairie  or  shrub  to  other  types  of  woodland.  In  the  mountains 
it  occupies  exposed  south  or  southwest  slopes  or  only  the  tops  of 
these  if  the  lower  slopes  are  sheltered.  Not  infrequently  it  is 
accompanied  by  Douglas  fir. 

On  the  exposed  buttes  only  scattered  trees  may  occur  among 
the  shrubs  on  north  slopes.  In  other  cases  well  developed  for- 
ests may  be  found.  On  higher  buttes,  the  rocky  tops,  ravines, 
and  sheltered  bases  may  be  clothed  with  a  pine  forest,  while  large 
stumps,  or  isolated  pines  towering  above  the  Douglas  fir  and  tam- 
arack now  in  possession  of  the  moist,  sheltered  slopes,  tell  the 
story  of  a  former  occupation  by  a  pine  forest.  Thus  all  stages 
of  development  are  strikingly  shown  on  these  butte  ramparts  of 
the  forest  frontiers.  Often  on  wind-swept  ridges  a  sheltering 
spur  permits  the  growth  of  pines,  while  a  slight  descent  from  a 
pine-clad  ridge  may  reveal  an  entire  change  in  tree  dominants, 
the  Douglas  fir  and  tamarack  replacing  the  pine. 

As  already  indicated,  the  pines  have  worked  their  way  down 
the  Palouse  River  and  along  Rock  Lake.  In  the  shallow  canyons 
they  are  practically  confined  to  the  sheltered  canyon  sides.  Doug- 
las fir  and  Larix  accompany  them  in  the  deeper  canyons  of  the 
Palouse  River,  but  I  have  found  only  the  former  with  the  pine 
about  Rock  Lake.  Opulaster  pauciflorus  invariably  accompanies 
these  forest  outposts  and  its  distribution  is  undoubtedly  due  to 
chipmunks  and  squirrels,  which  are  likewise  ever  present  in  pine 
woods.  Numerous  plants,  which  otherwise  are  found  only  in  the 
mountains  also  occur  in  these  pine-clad  canyons.  Among  others 
Aconitum  columbianum,  Actaea  spicata  arguta,  Thermo psis  mon- 
tana,  and  Veratrum  viride  may  be  mentioned.  In  fact,  the  study 
of  plant  populations  upon  wooded  buttes  isolated  by  a  distance 
of  from  only  a  few  to  several  miles  from  the  forests  proper  is 
fascinating  and  instructive,  but  one  into  which  we  can  not  well 
enter  here. 

The  xerophytic  conditions  under  which  the  pines  grow  about 

80 


Southeastern  Washington  and  Adjacent  Idaho. 


Si 


Rock  Lake  are  remarkable.  Upon  the  thin  soils  which  seem  able 
to  support  only  a  Poa-Polygonum  community  and  where  even  the 
bunch-grass  seems  dwarfed,  pine  seedlings  establish  themselves, 
rooting  in  the  crevices,  and  eke  out  an  existence  for  years.  On 
the  rocks  in  early  August,  everything  is  dry  and  burned.  Even 
Amelanchier,  cherry,  and  Spiraea  become  defoliated,  still  the 
pines  hold  on  until  relieved  by  the  advent  of  autumn  showers. 
Their  stunted  condition  stands  in  marked  contrast  to  their  well 
developed  companions  in  the  more  protected  places  with  deeper 
soil. 

In  the  open  park-like  growth  of  the  yellow  pine  in  the  moun- 
tains it  is  not  unusual  to  find  fine  clean-boled  trees  2.5—3  ^ee^  m 
diameter  towering  above  one  or  two  younger  generations.  In 
other  situations  the  forest  is  less  open,  and  is  then  usually  mixed 
with  Douglas  fir.  In  such  situations,  as  one  would  expect  in  a 
transition  region  from  prairie  to  forest,  the  ground  cover  is  com- 
posed more  largely  of  prairie  than  of  forest  forms.  The  follow- 
ing lists  indicate  the  more  important  shrubs  and  herbs  of  open 
pine  woods : 


Amelanchier  florida 
Arctostaphylos  uva-ursi 
Ceanothus  sanguineus 
Holodiscus  discolor 
Opulaster  pauciflorus 
Pachistima  myrsinites 
Prunus  emarginata 

Achillea  millefolium  lanulosa 
Agropyron  spicatum( including 

var.  inerme) 
Anemone  piperi 
Antennaria  dimorpha 
Antennaria  luzuloides 
Antennaria  racemosa 
Apocynum  pumilum 
Arnica  cordifolia 


Rosa  gymnocarpa 
Rosa  nutkana 
Salix  scouleriana 
Spiraea  corymbosa 
Symphoricarpos  racemosus 
Vaccinlum  macrophyllum 


Aster  conspicuus 
Astragalus  mortoni 
Bromus  marginatus 
Calamagrostis  rubescens 
Campanula  rotundifolia 
Deschampsia  elongata 
Deschampsia  calycina 
Drymocallis  convallaria 
Epilobium  angustifolium 


82  A  Study  of  the  Vegetation  of 

Erythronium  grandiflorum  Leptotaenia  multifida 

Fragaria  bracteata  Lupinus  laxiflorus 

Fragaria  platypetala  Lupinus  ornatus 

Frasera  fastigiata  Moehringia  macro phylla 

Galium  spp.  Pentstemon  pinetorum 

Geranium  viscosissimum  Potentilla  blaschkeana 

Helianthella  douglasii  Pteridium  aquilinum  pubescens 

Hieracium  albiflorum  Sedum  douglasii 
June  aides  campestre 

As  the  pine  forest  becomes  more  closed  the  shrubs  tend  to  dis- 
appear, and  usually  considerable  Douglas  fir  and  tamarack  are  to 
be  found.  The  transition  from  pine  to  the  pine-Douglas  mictium 
or  Douglas-Lamr  mictium  takes  place  in  this  manner.  Not  only 
has  the  closed  pine  forest  established  more  congenial  conditions 
for  tree  seedlings,  but  it  has  made  its  own  reproduction  difficult 
if  not  impossible  by  a  cutting  down  of  the  light  intensity.  In 
order  for  yellow  pine  to  thrive,  the  sun  must  strike  the  seedling 
the  greater  part  of  the  day.  Small  openings  in  forests  made  by 
the  removal  of  a  few  trees  by  windfall  or  natural  death  do  not 
furnish  sufficient  light.  However,  the  slightly  more  tolerant 
Douglas  fir  and  tamarack  can  not  only  grow  here,  but  actually 
shade  out  competing  pine  species.  Thus  the  physiognomy  of  the 
forest  may  gradually  change  from  pine  to  Douglas  fir  or  to  Doug- 
las fir  and  tamarack  with  all  intermediate  combinations  in  mic- 
tium. Consequently,  mixed  forests  of  pine  and  Douglas  fir  into 
which  Larix  is  invading  are  common.  The  shrubby  and  herbace- 
ous flora,  of  course,  is  intermediate  between  that  already  given 
and  that  of  the  more  mesophytic  Pseudotsuga-Larix  mictium  to 
be  described. 

The  Pseudotsuga  Consocies. — Well  developed  communities  of 
Douglas  fir  occupy  the  upper  exposed  slopes  in  the  mountains. 
Frequently  the  stand  is  90  per  cent,  or  more  pure  Douglas  fir  but 
lower  down  the  slopes  it  is  almost  invariably  mixed  with  Larix 
and  white  fir,  to  which,  along  the  ravines,  it  may  almost  entirely 
give  way.  Likewise,  in  more  open  places  it  is  accompanied  by 
yellow  pine. 

82 


Southeastern  Washington  and  Adjacent  Idaho.  83 

Where  the  growth  is  rather  pure,  the  trees,  a  foot  or  more  in 
diameter,  are  pruned  high  and  the  dense  shade  permits  of  a  very 
sparse  ground  cover.  In  such  situations,  the  light  intensity  may 
fall  to  o.oi  or  even  lower.  Except  for  a  few  specimens  of  Coptis 
occidentale,  Anemone  piperi,  Mo[ehringia  macrophylla,  Thalictrum 
occidentalis,  or  Vaccinium  macrophyllum  the  ground  may  be 
quite  bare.  Douglas  fir  grows  only  poorly  at  light  values  of  0.025. 
Such  forests  may  completely  surround  bare  rock-topped  moun- 
tain peaks,  but  more  often  give  way  to  shrubs  or  small  areas  of 
grass  land.  Except  in  such  situations  I  have  never  seen  Douglas 
fir  invading  prairie. 

Douglas  fir  is  far  more  common  in  mixture  with  Larix  and 
white  fir  than  in  forests  of  which  it  is  the  dominant.  The  per- 
centage of  Douglas  fir  is  usually  determined  by  the  slope  and  ex- 
posure and  consequent  soil  moisture.  While  Larix  and  white  fir 
do  not  grow  in  as  dry  soil  as  Douglas  fir,  the  latter  is  less  domi- 
nant in  moister  situations  because  of  its  greater  light  requirements. 
Larix  is  slightly,  and  white  fir  much  more  tolerant  than  Douglas 
fir. 

The  Larix- Abies  Associes 

This  associes  makes  up  by  far  the  most  important  forests  of 
the  region.  Great  stretches  of  moist  mountain  slopes  are  covered 
with  forests  of  which  either  Larix  or  Abies  are  dominant  or  more 
often  the  two  form  a  mictium.  The  Larix  consocies,  dominated 
by  Larix  occidentalis,  occupies  the  higher  slopes  of  lower  water 
content  intergrading  from  the  Douglas  fir  above  to  the  more  meso- 
phytic  white  fir-cedar  mixture  of  the  moister  slopes,  ravines,  and 
valleys. 

It  has  already  been  pointed  out  that  the  larch  is  only  slightly 
less  xerophytic  than  the  Douglas  fir.  Its  place  in  the  succession 
is  intermediate  between  the  Douglas  fir  and  the  white  fir.  Its 
ability  to  withstand  the  wind-storms  that  uproot  white  pine  and 
white  fir  is  an  index  of  a  well  developed  root  system,  and  this 
probably  accounts  for  its  ability  to  grow  in  soils  where  the  surface 
layers  are  quite  dry. 

The  absence  of  Larix  seedlings  in  a  mature  forest  shows  that 

83 


84  A  Study  of  the  Vegetation  of 

the  young  trees  can  not  endure  shade.  However,  openings  of 
greater  or  lesser  extent  constantly  occur  in  primeval  forests  due  to 
the  dropping  out  of  old  trees,  to  windfalls  or  to  fires.  Since 
Larix  seedlings  can  do  well  in  openings  where  the  sunlight  enters 
during  the  middle  of  the  day,  the  chances  for  reproduction  are 
always  present.  The  tamarack,  because  of  its  thick  bark,  is  dis- 
tinctly a  fire-resistant  tree,  often  remaining  unscathed  where 
white  pine  and  white  fir  are  killed.  Hence,  large  tracts  of  burned 
areas,  where  the  tamarack  was  abundant,  now  appear  to  form 
nearly  pure  Larix  communities.  However,  an  examination  of  the 
new  tree  populations,  together  with  comparisons  with  unburned 
contiguous  areas,  reveals  the  true  mixed  nature  of  the  original 
forest.  In  such  places  the  white  fir  is  especially  prominent. 

Abies  grandis  is  not  only  more  tolerant  of  shade  but  is  also  more 
mesophytic  than  the  larch.  I  have  not  infrequently  found  fir 
seedlings  in  shade  so  dense  as  to  exclude  all  other  trees  except 
the  cedar.  White  fir  seedlings  can  grow  in  light  as  low  as  0.02 
to  0.015.  Under  such  conditions,  however,  growth  is  poor.  While 
it  can  develop  in  open  places  in  rather  dry  soil,  it  is  more  exacting 
in  soil  moisture  requirements  than  either  Douglas  fir  or  Larix. 

The  position  of  Abies  in  the  normal  succession  is  beautifully 
illustrated  on  sheltered  slopes  of  outlying  mountain  spurs  and 
buttes.  Passing  from  the  dry  open  pine  forest  one  can  find  all 
stages  from  pine-Douglas  fir  mixture  dominated  first  by  the  pine, 
to  a  pine-fir-tamarack  mictium  where  the  tall,  spindly,  bushy- 
topped  pines,  many  of  which  are  dead,  tell  the  story  of  the  lost 
struggle  for  light.  Areas  of  higher  water  content  on  the  same 
slope  may  show  Pseudotsuga-Larix  mixtures  with  the  fir  losing  its 
dominance  and  Abies  grandis  appearing.  The  next  stage  is  that 
of  a  Larix-Abies  mictium  with  the  coming  in  of  cedar.  Charac- 
teristic plants  of  these  drier  Larix-Abies  forests  are  given  in  the 
following  lists : 

Ceanothus  sanguineus  Ribes  viscosissiwmm 

Holodiscus  discolor  Rosa  gymnocarpa 

Opulaster  pauciflorus  Rubus  parviflorus 

Pachistima  myrsinites  Salix  scouleriana 

84 


Southeastern  Washington  and  Adjacent  Idaho.  85 

V actinium  macrophyllum  Fragaria  platypetala 

Anemone  piperi  Linnaea  borealis  longiflora 

Arnica  cordifolia  Micromeria  chamissonis 

Calamagrostis  rubescens  Pyrola  picta 

Chimaphila  umbellata  Thalictrum  occidentale 

Coptis  occid entails  Trillium  ovatum 

Cytherea  bulbosa  Vagnera  amplexicaulis 
Fragaria  bracteata 

While  Opulaster  pauciflorus  is  the  most  abundant  undershrub 
in  the  pine  consocies,  in  the  Larix- Abies  community  it  remains 
only  as  a  relict.  It  is  not  unusual  to  find  areas  of  dead  nine- 
bark  under  a  growth  of  tamarack  or  white  fir. 

Ribes  viscosissimum  while  occurring  sparingly  in  the  earlier 
stages  of  succession  is  frequent  in  these  dry  fir-tamarack  forests 
but  is  a  more  typical  undershrub  of  the  more  mesophytic  fir- 
tamarack  community.  In  the  cedar  consociation  it  gives  way  to 
the  more  mesophytic  Ribes  lacustre. 

Likewise,  Arstostaphylos  uva-ursi,  common  in  pine  woods,  is 
seldom  found  here.  Linnaea  borealis  longiflora  replaces  it,  cover- 
ing large  areas  with  a  carpet  of  trailing  stems.  The  twin-flower 
is  less  abundant  in  the  deep  shade  of  well  developed  fir-tamarack 
forests  and  drops  out  completely  in  the  cedars. 

In  well  developed  forests  the  white  fir  not  infrequently  reaches 
a  diameter  of  2.5-3.5  feet,  while  neighboring  tamarack  trees  reach 
diameters  of  similar  proportions.  Likewise,  Douglas  fir  fre- 
quently attains  a  diameter  of  3  feet,  a  relatively  small  tree  com- 
pared with  the  dimensions  it  reaches  in  the  humid  Washington 
region  west  of  the  Cascades.  Under  the  closed  canopy  of  such  a 
forest,  shrubs  are  almost  excluded  and  herbaceous  plants  are  not 
abundant.  The  light  values  may  drop  to  an  intensity  of  only  o.oi 
or  even  0.007. 

In  more  open  places  a  poorly  developed  shrubby  layer  may 
overtop  an  upper  layer  of  herbaceous  plants,  which  like  the  former 
is  not  well  developed.  Indeed,  both  may  be  absent  and  then  a 
scattered  growth  of  low-growing  herbs  with  a  few  fungi  and 
mosses  may  partially  cover  the  ground.  The  sparse  growth  of. 

85 


86  A  Study  of  the  Vegetation  of 

fungi  as  well  as  such  saprophytes  as  Corallorhiza  spp.  and  Ptero- 
spora  andromedea  appears  meager  indeed  to  one  accustomed  to 
the  rich  fungal  flora  of  an  eastern  deciduous  forest. 

The  following  lists  indicate  the  shrubs,  herbs,  and  some  fungi 
commonly  found  in  well  developed  mesophytic  forests : 

Chimaphila  umbellata  Ribes  lacustre 

Lonicera  utahensis  .  Rosa  pisocarpa 

Menziesia  ferruginea  Rubits  parviflorus 

Pachistima  myrsinites  Sambucits  melanocarpa 

Pyrus  sitchensis  Vaccinium  macrophyllum 

Ribes  i'iscosissimum 

Actaea  spicata  arguta  Linnaea  borealis  longi flora 

Adenocaulon  bicolor  Mitella  stauropetala 

Anemone  piperi  Osmorhiza  dlvaricata 

Arnica  cordifolia  Pyrola  spp. 

Asarum  caudatum  Streptopus  majus 

Clintonia  uniflora  Thalictrum  occidentale 

Coptis  occidentalis  Tiarella  unifoliata 

Disporum  majus  Trillium  ovatum 

Fragaria  spp.  Vagnera  amplexicaulis 
Galium  spp. 

Boletus  sp.  Morchella  bispora 

Clavaria  spp.  Morchella  spp. 

Coprinus  comatus  Peziza  spp. 

Gyromitra  esculenta  Sarcosoma  globosum 

These  changes  in  the  shrubby  and  herbaceous  populations  from 
the  less  mesophytic  to  the  more  mesophytic  members  as  the  suc- 
cession advances  are  no  less  characteristic  than  the  changes  in  the 
lichen  flora  which  abounds  on  the  trees.  While  in  open  pine 
woodland  the  trees  are  often  covered  with  the  yellowish  and  gray- 
ish patches  of  Letharia  vulpina  and  Parmelia  physodes,  in  the 
early  stages  of  the  Douglas  fir-tamarack  community  these  lichens 
give  way  especially  to  species  of  Alectoria.  Of  these  the  long 
pendant  thallus  of  A.  fremonti  is  especially  characteristic,  while 

86 


Southeastern  Washington  and  Adjacent  Idaho.  87 

A.  oregana  is  less  abundant.  As  conditions  become  more  meso- 
phytic  in  the  Larix- Abies  community,  Usnea  dasypoga  begins  to 
predominate,  while  in  the  climax  cedar  consociation  the  trees  are 
often  beautifully  draped  with  the  long  yellow  strands  of  this 
species.  Under  such  conditions  species  of  Alectoria  are  not  fre- 
quent. 

Other  trees  which  are  more  or  less  important  components  of 
these  forests  are  the  white  pine,  Pinus  monticola,  lodgepole  pine, 
Pinus  murrayana,  yew,  Taxus  brevifolia,  and  Engelmann  spruce, 
Picea  engelmanni. 

The  white  pine,  although  more  abundant  and  of  greater  value 
on  the  bottom  lands  of  streams  in  northern  Idaho  than  anywhere 
throughout  its  range,  is  not  an  important  tree  in  the  area  under 
consideration.  It  occurs  only  sparingly  throughout  and  where  it 
is  best  developed  on  the  moister  slopes,  seldom  makes  up  more 
than  5  per  cent,  of  the  forest  and  reaches  this  abundance  in  only 
local  areas.  It  appears  to  require  a  moister  soil  than  white  fir,  but 
its  seedlings  can  stand  considerable  shading.  Perhaps  the  dry- 
ness  of  the  climate  combined  with  the  ravages  of  forest  fires 
which  may  kill  it  and  leave  larch  and  red  fir  uninjured,  combined 
to  make  it  an  unsuccessful  tree  in  this  region. 

The  lodgepole  pine,  Pinus  murrayana,  occurs  very  sparingly 
throughout  the  western  forest  frontier  of  the  region.  Eastward 
and  northward,  especially  in  cut-over  and  burned-over  regions,  it 
assumes  considerable  importance,  occurring  in  mixture  through- 
out all  types  of  forest,  and  frequently  forming  dense  even  stands 
over  considerable  areas.  Unlike  the  yellow  pine  it  seldom  plays 
the  role  of  pioneering  in  grass  land  and  since  it  is  distinctly  a  "  fire 
tree "  of  a  weedy  nature,  it  had  best  be  considered  in  another 
place. 

Taxus  brevifolia  is  very  rare  in  this  region,  occurring  only  oc- 
casionally along  ravines  and  then  taking  on  only  a  scrubby  form. 
Its  role  in  the  forests  of  the  region  is  insignificant. 

Engelmann  spruce,  so  characteristic  of  high  mountain  slopes 
elsewhere,  while  never  found  in  great  abundance,  is  rather  a  fre- 
quent forest  tree  at  the  highest  altitudes,  especially  in  wet  ravines 
and  about  the  edges  of  alder  swamps.  It  does  best  in  soils  where 

87 


88  A  Study  of  the  Vegetation  of 

the  deeper  strata  are  very  moist.  Outside  of  meso-hydrophytic 
situations  it  does  not  flourish  in  the  region  and  even  here  it  does 
not  reach  the  usual  size  of  the  species.  It  sometimes  forms  a 
very  broken  and  fragmentary  zone  between  the  alder-willow  com- 
munity and  the  climax  cedar  forest.  Its  ability  to  tolerate  shade 
to  a  greater  degree  than  Douglas  fir  or  tamarack  probably  ac- 
counts for  the  presence  of  its  seedlings  in  drier  situations,  for  I 
have  shown  that  conditions  under  typical  stands  of  white  fir  and 
tamarack  are,  as  regards  the  seedling  stage,  fairly  mesophytic. 
Likewise,  its  power  to  germinate  in  the  open,  providing  there  is 
sufficient  soil  moisture,  accounts  for  its  presence,  often  in  dense 
stands,  in  situations  where  drifts  of  melting  snow  keep  the  soil 
well  moistened  in  otherwise  apparently  rather  dry,  rocky  situ- 
ations. Like  other  shade-enduring  species,  it  makes  a  more  rapid 
growth  in  these  situations  than  in  the  shade. 

The  Thuja  Consociation 

The  climax  forest  community  of  the  region  and  the  one  in  the 
xerosere  with  the  lowest  light  intensity,  greatest  soil  and  air 
humidity  as  well  as  lowest  temperature,  is  that  dominated  by  the 
cedar,  Thuja  plicata.  The  best  protected  and  most  mesophytic 
mountain  slopes  as  well  as  the  well  watered  ravines  are  clothed 
with  a  growth  of  this  cedar.  These  often  form  90  per  cent,  or 
more  pure  stands  and  the  trees  may  reach  diameters  of  3-5  feet. 
In  such  well  developed  forests,  the  light  intensity  ranges  from 
0.015  to  0.005  and  even  to  0.003,  and  except  for  the  seedlings  of 
the  cedar  the  ground  may  be  quite  bare.  But  usually  the  forest 
canopy  is  sufficiently  open  to  permit  a  growth  of  a  few  shade- 
enduring  shrubs  and  numerous  herbs.  Of  these  the  following  are 
typical  of  the  consociation : 

Ribes  lacustre  Rubus  parviflorus 

Aconitum  columbianum  Circaea  pacific  a 

Anemone  piperi  Claytonia  asarifolia 

Asarum  caudatum  Clintonia  uniflora 

Athyrium  cyclosorum  Coptis  occidentalis 

88 


Southeastern  Washington  and  Adjacent  Idaho.  89 

Galium  sp.  Viola  glabella 

Streptopus  ma  jus  Viola  orbiculata 

Tiarella  unifoliata  Vagnera  ample  xicaulis 
Trillium  ovatum 

The  high  humus  content  and  consequent  great  water  holding 
capacity  of  the  soil  is  probably  due  in  part  to  the  lack  of  forest 
fires.  For  it  is  easy  to  see  how  the  more  moist  areas  in  the  deep 
ravines  would  be  less  subject  to  burning  than  the  drier  slopes 
with  their  proportionally  greater  amount  of  undershrubs.  The 
forest  floor  supports  the  best  developed  fungus  flora  of  the  region. 
This  includes  species  previously  enumerated.  However,  even 
here  the  fungus  flora  is  relatively  scanty. 

Because  of  the  shade  the  trees  are  often  pruned  high,  while  the 
branches  are  draped  with  long  strands  of  Usnea.  Often  at  higher 
altitudes  Picea  engelmanni  accompanies  the  cedar  down  the  moist 
ravines  but  never  assumes  very  great  importance. 

The  greater  mesophytism  and  tolerance  of  the  white  fir  as  con- 
trasted with  that  of  the  tamarack  and  Douglas  fir  are  shown  by  the 
presence  of  the  former  in  the  mixed  cedar-white  fir  forest.  It  is 
the  last  of  these  trees  to  give  way  to  the  cedar,  certain  communi- 
ties showing  gigantic  relict  white  firs  while  all  of  the  saplings  are 
those  of  the  cedar.  Proceeding  up  the  slope  from  a  cedar  com- 
munity the  white  firs  become  dominant  as  the  cedars  become 
smaller  and  less  frequent  on  the  drier  soil,  then  a  zone  of  white 
fir  and  tamarack  is  passed,  while  further  up  in  this  mixture 
Douglas  fir  becomes  more  abundant.  Of  course,  the  illustration 
is  rather  overdrawn  for  the  accidents  of  windfalls,  and  especially 
fires,  may  often  greatly  alter  these  conditions. 

The  formation  as  a  living  developing  entity  has  reached  its 
maturity  in  the  cedar  consociation.  Because  of  the  low  light 
intensity  the  establishment  of  the  seedlings  of  the  other  forest 
trees  of  the  region  in  the  cedar  community  is  impossible.  Hence, 
the  adult  stage  will  go  on  indefinitely  repeating  itself  generation 
after  generation,  unless  disturbed  by  some  outside  factor  as  a 
forest  fire  or  the  hand  of  man. 

Having  traced  the  normal  development  of  the  forest  through  the 


90  A  Study  of  the  Vegetation  of 

xerosere  to  its  climax  community,  we  will  next  consider  briefly 
a  hydrophytic  adsere,  after  which  we  will  take  up  the  secondary 
succession  or  subsere. 

The  Adsere.    Alnus-Salix  Associes 

Distinctly  hydrophytic  plant  communities  characterized  by 
Alnus  sinuata,  Salix  scouleriana,  and  Pyrus  sitchensis  occupy 
broad  wet  ravines  and  springy  places  often  high  up  on  the  moun- 
tain sides.  The  weight  of  the  great  banks  of  snow  which  drift 
over  the  trees  and  sometimes  almost  bury  them,  pushes  them  into 
a  semi-procumbent  position  leaning  down  the  slope.  The  alder, 
which  is  usually  dominant,  reaches  a  diameter  of  2-5  inches  and 
a  vertical  height  of  only  12  or  15  feet,  while  not  infrequently  it 
attains  a  length  greater  than  twice  its  height.  Likewise,  the 
willow  and  mountain  ash  and  also  the  mountain  maple,  Acer 
glabrum  douglasii,  which  accompany  it  in  this  habitat,  are 
bent  down  the  slopes  by  the  weight  of  the  snow.  Because  of 
the  late  melting  of  the  snow  in  such  situations  and  the  resulting 
springy  nature  of  the  soil,  coniferous  tree  seedlings  are  excluded. 
Engelmann  spruce,  as  already  indicated,  often  borders  such  alder 
thickets  and  in  turn  gives  way  to  the  cedar. 

In  this  tangle  of  semi-prostrate  trees,  shrubs  are  nearly  ex- 
cluded, although  Sambucus  melanocarpa  and  Ribes  lacustre  occur 
rather  infrequently.  A  dense  herbaceous  undergrowth  which 
almost  completely  conceals  the  ground  is  made  up  of  the  follow- 
ing mesophytic  species : 

Aconitum  columbianum  Disporum  oreganum 

Actea  spicata  arguta  Mertensia  membranacea 

Athyrium  cyclosorum  Osmorhiza  divaricata 

Circaea  pacifica  Senecio  triangularis 

Claytonia  asarifolia  Streptopus  amplexifolius 

Clintonia  uniftora  Thalitfrum  occidentale 

Disporum  ma  jus  Trillium  ovatum 

The  preceding  plant  species  together  with  certain  other  meso- 
phytic shrubs  and  herbs  and  hydrophytic  mosses  border  the  moun- 

90 


Southeastern  Washington  and  Adjacent  Idaho.  91 

tain  streams,  which,  indeed,  may  be  fringed  with  a  more  or  less 
fragmentary  alder  community. 

SUBSERE.  REFORESTATION  OF  CUT-OVER  AREAS  AND 

BURNS 

Since  the  direction  of  development  is  always  forward  and 
toward  the  climax  community  of  a  region,  the  removal  of  the 
plant  cover,  such  as  a  forest,  makes  possible  the  repetition  of 
the  story  of  normal  succession.  This,  however,  may  be  consider- 
ably modified  and  the  amount  of  repetition  determined  by  the 
degree  of  completeness  of  the  destruction. 

In  studying  the  natural  reforestation  of  the  region,  it  will  be 
advantageous  to  consider  first  the  secondary  succession  or  sub- 
sere  after  cutting,  and  afterwards  the  reestablishment  of  forests 
following  burns. 

Naturally  many  of  the  outlying  pine-covered  areas  were  early 
cleared  by  the  settlers  and  the  land  used  for  the  cultivation  of 
crops.  Where  small  tracts  have  been  allowed  to  "  go  back  "  after 
removing  the  yellow  pine  and  burning  the  brush,  the  first  years 
show  a  rapid  growth  of  shrubs  while  the  intervening  spaces  are 
dominated  largely  by  prairie  species.  Opulaster  pauciflorus, 
Spiraea  corymbosa  and  other  shrubs,  which  in  the  denser  stands 
have  been  suppressed  by  the  shade,  spring  rapidly  into  dominance, 
while  Epilobium  angustifolium,  Cirsium  palousense,  Pteridium 
aquilinum  pubescens,  and  Deschampsia  spp.  mingle  with  various 
prairie  species  already  designated  as  occurring  in  yellow  pine 
forests.  Among  these,  yellow  pine  seedlings  grow  vigorously 
and  the  forest  finally  reestablishes  itself.  Of  course,  repeated 
fires  kill  the  pine  seedlings,  burn  off  the  shrubs,  and  favor  the 
invasion  of  prairie  plants.  Although  prairie  fires  in  the  Palouse 
Region  were  never  so  severe  as  those  of  the  Great  Plains,  it  is 
probable  that  they  played  an  important  role  in  preventing  the  in- 
vasion of  conifers  into  the  grass  land. 

In  most  of  the  more  accessible  canyons  of  the  mountains, 
lumbering  has  been  carried  on  and  in  some  places  the  operation 
of  the  lumberman  has  been  followed  by  ground  fires.  In  prac- 
tically all  cases,  except  in  the  lodgepole  region  eastward,  where 

91 


92  A  Study  of  the  Vegetation  of 

reforestation  has  occurred,  the  new  forest  has  usually  about  the 
same  composition  as  the  old.  In  these  cases,  the  composition 
of  the  previous  forest  was  determined,  of  course,  by  a  study 
of  the  stumps,  by  checking  with  the  adjacent  forest,  especially 
primeval  forest  areas  on  similar  adjacent  slopes.  The  following 
case,  found  by  repeated  trials  to  be  rather  typical,  is  illustrative. 

Belt  transects  through  a  second  growth  forest  occupying  an 
area  in  Thatuna  Hills  cut  over  about  twenty-five  years  ago  gave 
the  following  percentage  composition  : 

Moist  North  Slope  Dry  South  Slope 

Yellow  pine  0.5  per  cent.  Yellow  pine  36.0  per  cent. 

Douglas  fir    4.0  per  cent.  Douglas  fir    14.0  per  cent. 

Tamarack   30.0  per  cent.  Tamarack   10.0  per  cent. 

White  fir    26.0  per  cent.  White  fir   40.0  per  cent. 

Cedar   39.5  per  cent. 

Superficially  such  moist  slopes  appear  to  be  clothed  with  nearly 
a  pure  tamarack  forest,  due  to  the  more  rapid  height-growth  of 
this  species.  In  such  young  forests  the  cedars  are  often  small, 
in  fact,  many  are  mere  seedlings.  A  count  of  the  annual  rings 
shows  that  they  came  in  after  the  other  trees  had,  by  their  shade, 
made  conditions  less  xerophytic.  Their  importance  in  the  general 
composition  of  the  forest  might  be  overestimated  from  their  high 
percentage.  Farther  up  the  slopes  they  are  scattering,  and  only 
near  the  moist  base  are  they  present  in  great  abundance.  Like- 
wise, the  white  fir  on  the  south  slope  occurs  mostly  in  dense 
thickets  near  the  base.  On  the  open  south  slope  trees  averaged 
only  i  per  square  meter,  while  on  the  north  slope  the  average  was 
3.5  per  unit  area. 

No  less  characteristic  of  the  two  types  of  forests  are  the  shrubs 
and  herbs  of  the  undergrowth.  Opulaster  pauciflorus,  Ceanothus 
velutinus,  and  Salix  scouleriana  make  up  the  chief  shrubby  growth 
on  the  south  slope,  often  covering  many  square  meters  exclusively. 
On  the  north  slope  both  Opulaster  pauciflorus  and  Ceanothus 
velutinus  occur  but  rarely,  while  Vaccinium  macrophyllum  is 
more  abundant  than  Salix  scouleriana.  Coptis  occidentals, 
Clintonia  uniflora,  Thalictrum  Occident  ale }  Mitella  stauropetala, 

92 


Southeastern  Washington  and  Adjacent  Idaho.  93 

Galium  sp.,  Asarum  caudatum,  Anemone  piperi,  Pyrola  bracteata, 
Cytherea  bulbosa,  and  species  of  Vagnera,  all  found  here,  are 
typical  plants  of  the  moister  slopes,  and  contrast  markedly  with 
Calamagroftis  rubescens,  Bromus  marginatus,  Pteridium  aqui- 
linum  pubescens,  Pentstemon  pinetorum,  Astragalus  mortoni,  Aster 
conspicuus,  Anaphalis  margaritacea  occidentals,  Antennaria 
racemosa,  Pedicularis  racemosa,  and  Berberis  repens,  found  on 
the' more  open  south  mountain  side. 

Cut-over  areas  in  the  northeast  part  of  the  region,  where  as 
a  result  of  fires  lodgepole  pine  is  frequently  abundant,  showed  in 
addition  to  the  usual  herbaceous  and  shrubby  growth  and  tree 
seedlings  of  all  the  common  tree  species,  a  frequent  dominance  of 
Pinus  murrayana.  The  numerical  dominance  is  a  result  of  its 
prolific  seeding  habit,  brush  fires  being  sufficient  to  open  many 
of  the  cones,  while  its  rapid  height-growth  makes  it  stand  out 
prominently  when  mixed  with  other  species.  The  developmental 
history  of  such  areas  will  be  considered  under  reforestation  of 
burns. 

A  report  of  the  study  of  the  natural  reforestation  of  burned 
areas  in  the  mountains  of  northern  Idaho  has  already  been  made 
(6).  Although  much  of  the  area  there  included  lies  outside  of 
the  boundaries  of  the  present  investigation,  still  conditions  are  so 
similar  that  a  brief  statement  may  be  included  here. 

During  the  month  of  August,  1910,  the  greater  part  of  northern 
Idaho  and  much  of  eastern  Montana  was  swept  by  one  of  the 
most  extensive  and  destructive  forest  fires  ever  experienced  in 
that  part  of  the  country.  In  many  heavily  wooded  canyons  the 
draft  was  so  violent  during  the  fire  and  the  heat  so  intense  as  to 
destroy  every  vestige  of  life  above  ground. 

The  town  of  St.  Maries,  Idaho,  lies  against  the  slopes  of  foot- 
hills, which,  prior  to  1910,  were  covered  with  a  more  or  less  mixed 
forest  of  coniferous  trees  comprising  the  following  species :  Pseu- 
dotsuga  mucronata,  in  practically  all  situations ;  Pinus  ponderosa, 
abundant  on  south  slopes  and  in  exposed  and  rocky  situations ; 
Larix  occidentalis  associated  with  Abies  grandis  and  Pseudo- 
tsuga;  Pinus  monticola  and  Thuja  plicata  accompanied  by  indi- 

93 


94  A  Study  of  the  Vegetation  of 

viduals  of  Pseudotsuga  and  Abies,  confined  generally  to  the 
canyons  and  rich  levels  at  the  bases  of  north  slopes. 

These  mountain  slopes  were  overrun  by  fire  on  August  21  and 
22,  1910.  As  they  seemed  to  represent  fairly  the  average  forest 
conditions  for  northern  Idaho,  it  was  decided  that  here  would  be 
a  most  satisfactory  place  to  carry  on  a  study  of  the  problem  of 
natural  reforestation. 

Among  the  first  pioneers  to  reclaim  the  unshaded  and  charred 
soil  were  Funaria  hygromWrica  and  Marchantia  polymorpha. 
Cirsium  palousense,  Erigeron  acris,  and  Epilobium  angustifoUum 
were  the  chief  herbs,  whose  wind-blown  fruits  afforded  them  an 
early  entrance.  Likewise,  the  numerous  seedlings  of  Sdix 
scouleriana  may  be  accounted  for  in  the  same  manner,  while 
numerous  others  sprang  up  from  the  underground  parts  of  the 
older  willows  characteristic  of  more  open  areas.  The  presence  of 
Opulaster  pauciflorus,  Arnica  cordifolia,  and  Erythronium  grandi- 
florum  may  likewise  be  accounted  for  by  the  fact  that  the  fire 
left  unharmed  the  rootstocks  of  the  shrub  and  of  Arnica  and  the 
corms  of  the  lily. 

In  the  spring  of  1911  and  the  second  year  after  the  fire,  Epi- 
lobium angustifoUum  was  predominant  everywhere.  The  indi- 
viduals varied  from  mere  seedlings  to  plants  12-18  inches  in 
height,  often  as  many  as  30  to  50  individuals  occurring  in  a  single 
square  meter.  Thousands  of  the  smallest  were  succumbing  to  an 
epidemic  of  Aecidium.  Next  in  importance  to  the  fireweed  was 
the  thistle,  Circium  palousense,  which  with  Antennaria  lusuloides 
and  the  species  enumerated  as  occurring  the  preceding  year, 
formed  a  considerable  herbaceous  carpet  over  the  burned  area. 
Every  inch  of  the  ground  otherwise  unoccupied  seemed  covered 
with  Funaria  hygrometrica.  The  following  shrubs,  Opulaster 
pauciflorus,  Rosa  gymnocarpa,  and  Rubus  parviflorus,  which  were 
more  or  less  abundant,  had,  like  several  of  the  herbs  in  the  fol- 
lowing list,  been  able  to  survive  the  fire  by  means  of  underground 
propagative  parts.  The  bulbs  of  ZygadenusvenenosusandFritil- 
laria  lanceolata,  and  the  corms  of  Erythronium  grandiflorum,  all 
of  which  were  present  in  considerable  abundance,  were  found  at 
depths  of  5-7  inches  below  the  surface  of  the  soil.  Other  plants 

94 


Southeastern  Washington  and  Adjacent  Idaho.  95 

present  in  greater  or  lesser  abundance  were  Potentilla  sp.,  Mitella 
stauropetala  (abundant),  Leptotaenia  multifida,  Disporum  ma  jus, 
Moehringia  macrophylla,  Coptis  occidentalis,  Viola  spp.,  two 
species  of  Lathyrus,  and  Vicia  sp. 

It  is  of  interest  here  to  note  that  in  spite  of  the  terrific  heat 
which  must  have  prevailed  over  those  mountain  slopes,  except 
where  the  undergrowth  was  dense,  a  considerable  depth  of  humus 
remained  intact.  Where  this  was  wholly  consumed  and  the  soil 
had  been  washed  bare  by  rains  there  was  a  fairly  complete  turf 
of  F unarm  and  Marchantia  along  with  certain  herbaceous  plants 
already  given.  The  effects  of  this  forest  fire  were  more  pro- 
found in  certain  parts  of  the  forest  than  in  others,  depending 
somewhat  upon  the  topography  of  the  devastated  region.  In  the 
"  draws  "  or  small  lateral  canyons  where  growth  conditions  were 
such  as  to  produce  the  most  excellent  stand  of  white  pine,  Douglas 
fir,  white  fir,  and  cedar,  the  fire  was  most  destructive,  leaving  no 
trees  alive.  Whereas,  on  lateral  or  secondary  ridges  it  was  fre- 
quently observed  that  from  25  to  75  per  cent,  of  these  species,  in- 
cluding yellow  pine,  survived  the  heat.  These  constituted  the 
seed  trees  so  valuable  in  the  reforestation  now  going  forward. 

A  diligent  search  was  made  for  any  seedlings  of  the  cone- 
bearing  trees  characteristic  of  the  region  under  observation,  and 
a  few  were  found.  A  limited  number  of  these  (all  were  Larix 
occidentalis}  were  from  seed  germinated  in  1911,  but  the  majority 
were  but  a  few  weeks  old  at  the  time  of  observation.  They  were 
indeed  scarce — not  more  than  60-80  per  acre  on  north  and  east 
slopes  and  none  at  all  on  south  and  southeast  or  southwest  ex- 
posures. In  two  instances  it  was  observed  that  as  many  as  15-20 
seedlings  were  growing  in  one  spot  as  though  a  cone  had  become 
planted  and  all  its  viable  seeds  had  germinated.  The  area  in- 
vestigated seemed  to  show  no  signs  of  any  other  conifer,  which 
fact  corroborates  observations  of  a  similar  nature  made  in  cer- 
tain denuded  sections  of  Thatuna  Hills.  However,  by  the  fall 
of  the  same  year,  many  seedlings  of  Thuja,  Larix,  Pseudotsuga, 
and  a  few  of  Abies  had  sprung  into  existence. 

It  is  probable  that  some  of  these  seeds  were  furnished  by 
scattered  surviving  parent  trees  in  the  vicinity,  although  it  is 

95 


96  A  Study  of  the  Vegetation  of 

equally  certain  that  others  buried  in  the  moister  duff  escaped  burn- 
ing.  Hoffman  (7)  has  shown  that  seeds  of  Thuja  plicata  may 
remain  dormant  in  the  soil  for  two  years,  while  those  of  Pinus 
monticola  and  Pseudotsuga  mucronata  may  be  buried  in  the  duff 
for  six  years  and  still  remain  viable. 

The  distribution  of  the  seedlings  was  very  irregular.  In  some 
areas  of  a  square  meter  or  more  none  could  be  found,  while  in 
other  more  favored  spots  the  seedlings  would  average  as  many 
as  8  per  square  meter.  The  ground  occupied  by  these  seedlings 
was  well  covered  with  a  mulch  of  the  dead  leaves  and  stems  of 
such  herbaceous  plants  as  have  already  been  described  for  the 
region. 

On  the  denuded  south  slopes  where  the  original  forest  growth 
consisted  of  an  abundant  stand  of  Pinus  ponderosa  with  scattered 
individuals  of  Pseudotsuga  mucronata,  notwithstanding  the  pres- 
ence of  a  growth  of  Symphoricarpos,  Pteridium,  Epilobium, 
Cirsium,  Achillea,  and  other  plants  in  considerable  abundance 
and  so  intermingled  as  to  form  a  semi-shaded  protected  area,  no 
coniferous  seedlings  were  present.  Their  absence  was  no  doubt 
due  to  insufficient  soil  moisture  and  excessive  evaporation. 

These  south  mountain  sides  and  their  ravines  and  canyons  will 
in  the  course  of  time  be  reclaimed  by  a  new  growth  of  yellow  pine 
and  Douglas  fir  unless  ground  fires  occur  and  natural  growth 
conditions  are  obliterated. 

Reforestation  studies  in  areas  swept  by  fires  of  all  degrees  of 
severity  were  made,  especially  in  Thatuna  Hills.  In  some  cases 
only  very  local  areas  were  concerned,  while  in  others  the  fires 
covered  considerable  territory  (Fig.  43).  In  practically  all  cases 
sufficient  seed  trees  were  either  left  standing  in  the  burned  area 
or  on  unburned  ridges  in  close  proximity  to  furnish  the  seed  for 
reforestation. 

About  twenty-nine  years  ago,  many  square  miles  of  these  hills 
were  overrun  by  a  fire  which  destroyed  more  or  less  completely 
much  of  the  virgin  timber,  leaving  here  and  there  a  few  living 
trees  representing  the  different  species  to  serve  as  seed  trees  in 
subsequent  years.  These  burns  covered  chiefly  the  north  and 
northeast  slopes  of  the  mountains.  In  these  mixed  forests  of 


Southeastern  Washington  and  Adjacent  Idaho.  97 

white  fir,  tamarack,  Douglas  fir,  and  cedar,  the  thick-barked 
tamarack  suffered  least,  and  often  only  the  trees  of  this  species 
less  than  6-8  inches  in  diameter  were  killed.  This  gave  rise  to 
what  are  apparently  nearly  pure  forests  of  tamarack ;  but  in  most 
cases  sufficient  seed  trees  of  the  other  species  were  left  to  in- 
sure re-seeding,  and  at  present  a  new  generation  of  white  fir  and 
tamarack  are  especially  prominent. 

Notwithstanding  the  now  open  nature  of  the  forest,  the  ground 
being  covered  with  the  blackened  and  charred  remains  of  fallen 
white  firs  and  cedars,  many  of  the  smaller  tamaracks,  though 
dead,  are  still  standing.  The  larger  ones,  often  fire  scarred,  but 
living,  are  not  usually  more  than  12-14  inches  in  diameter.  They 
reach  a  height  of  85-100  feet,  and,  like  the  fir,  reveal  by  their 
high  pruning  a  former  forest  with  a  closed  canopy. 

On  the  upper  and  middle  slopes  the  ground  is  more  or  less  com- 
pletely covered  by  a  thin  layer  of  raw  humus,  consisting  mostly 
of  the  leaves  of  the  tamarack.  Numerous  quadrats  in  various 
areas  revealed  a  predominance  of  the  seedlings  of  the  white  fir, 
often  20-25  per  square  meter,  while  Douglas  fir  and  tamarack 
were  less  abundant.  In  many  places  the  mineral  soil  was  destitute 
of  vegetation,  while  only  a  sparse  growth  represented  by  Hier- 
acium  albiflorum,  Clintonia  uni flora,  Adenocaulon  bicolor,  Galium 
sp.,  Chimaphila  umbellata,  Micromeria  chamissonis,  Pyrola  picta, 
and  a  few  other  scattered  species  occurred  elsewhere. 

The  severe  conditions  under  which  the  tree  seedlings  were 
growing  were  shown  by  the  fact  that  even  the  oldest,  which  came 
in  at  least  three  or  four  years  after  the  fire,  did  not  exceed  a 
height  of  15-18  inches. 

Judging  from  adjoining  and  unburned  forests  of  a  similar  com- 
position it  appears  that  the  remaining  tamaracks  by  a  spreading 
of  their  crowns  had  considerably  increased  the  shade,  the  light 
value  often  falling  to  0.2,  and  thus  offering  considerable  protec- 
tion to  the  tree  seedlings. 

Farther  down  on  similar  slopes,  where  the  fire  left  fewer  trees 
standing,  both  because  fewer  tamarack  trees  were  present  and 
because  the  fire  was  more  severe,  quite  a  different  stage  in  repro- 
duction is  to  be  seen.  Here,  because  of  more  moisture  and  the: 

97 


98  A  Study  of  the  Vegetation  of 

open  light,  average  major  quadrats  revealed  as  many  as  200  tree 
seedlings.  Of  these  nearly  four-fifths  were  white  fir  and  tam- 
arack, about  equally  distributed,  while  the  rest  were  Douglas  fir, 
white  and  yellow  pine.  Many  of  these  were  19-20  years  old,  with 
a  height-growth  of  6-13  feet,  the  tamarack  as  usual  in  the  lead. 
In  the  moist  ravines  young  cedars  were  abundant.  The  early  his- 
tory of  this  forest  was  probably  the  same  as  that  of  the  St.  Maries 
region  already  described. 

In  heavy  burns  in  other  parts  of  the  region  where  big  cedar, 
spruce,  white  fir,  and  tamarack  timber  have  been  completely  de- 
stroyed, various  species  of  shrubs,  especially  V actinium  macro- 
phyllum,  Menziesia  ferruginea,  Salix  scouleriana,  and  thickets  of 
Alnus,  Rubus  parviflorus,  Ribes'  lacustre,  Rubus  macro  petahis, 
and  maple  had  sprung  up  and  almost  completely  covered  with 
their  dense  growth  the  fire  blackened  tangle  of  fallen  trees.  How- 
ever, they  form  a  good  protection  for  the  tolerant  cedar  and 
spruce,  and  while  they  may  shade  out  other  seedlings  for  a  time, 
still  there  are  always  openings,  and  especially  in  drier  soil  where 
the  less  tolerant  but  also  the  less  exacting  fir  and  larch  can  get  a 
foothold. 

Without  further  details  the  general  story  of  reforestation  of 
burns  in  the  region  is  as  f olows :  Soon  after  the  fire  the  ground 
is  more  or  less  completely  covered  with  cryptogamic  vegetation  of 
which  Funaria  hygrometrica  and  Marchantia  polymorpha  are 
dominant.  Soon  plants  with  wind-blown  fruits  appear.  Of  these 
the  following  are  most  important: 

Epilobium  spicatum  Hieracium  albiflorus 

Salix  scouleriana  Antennaria  luzuloides 

Cirsium  palousense  Anaphalis  margaritaceae  occi- 
Erigeron  acris  dentalis 

Certain  grasses,  as  Bromus  marginatus,  and  fire  grass,  Agrostis 
hyemalis,  may  predominate  for  a  time  but  later  give  way  to  other 
herbaceous  growths,  especially  of  Epilobium  (Fig.  44).  After 
one  or  more  years,  varying  with  the  severity  of  the  burn  and 
degree  of  exposure,  tree  seedlings  begin  to  become  established. 

98 


Southeastern  Washington  and  Adjacent  Idaho.  99 

These  may  be  shaded  by  too  dense  thickets  of  various  shrubs, 
which  may  spring  up  from  underground  parts,  and  largely  re- 
place the  herbaceous  vegetation.  But  usually  the  shrubs  form  a 
protection  against  wind  and  excessive  evaporation.  The  trees  in 
turn  suppress  the  shrubs  and  the  'mature  forest,  usually  similar 
to  the  one  preceding,  is  replaced. 

Studies  of  reforestation  in  burns  of  varying  severity  show 
more  or  less  incompletely  the  several  stages  of  the  subsere.  How- 
ever, continued  investigation  in  these  and  in  completely  burned 
areas  indicates  the  following  serai  stages,  some  of  which  may  be 
telescoped  or  even  lacking  in  any  one  particular  burned  area. 

Salix-V actinium  ASSOCIES 

V actinium  consocies 

Rubus  consocies 

Salix  consocies 
Epilobium-Cirsium  ASSOCIES 

Cirsium  consocies 

Epilobium  consocies 
Agrostis-Bromus  ASSOCIES 

Bromus  consocies 

Agrostis  consocies 
Funaria-Marchantia  ASSOCIES 

Marchantia  consocies 

Funaria  consocies 

There  remains  only  to  be  considered  briefly  reproduction  in 
the  burns  in  the  northeastern  part  of  the  area  and  especially 
along  the  Palouse  River  where  the  lodgepole  pine  plays  a  sig- 
nificant role.  The  wide  range  of  the  lodgepole  habitat  from  very 
moist  to  very  dry  soil,  its  rapid  growth  and  early  reproduction  as 
well  as  its  inability  to  withstand  fires  or  to  endure  shade  are  too 
well  known  to  necessitate  discussion  here. 

The  forests  of  this  part  of  the  region,  where  lumbering  oper- 
ations have  been  going  on  for  a  long  time  and  burns  of  all  ages 
occur,  are  mixed  throughout  with  lodgepole  pine,  the  amount  of 
which  may  vary  from  a  few  towering  relict  trees  to  nearly  pure 
stands. 

99 


ioo  A  Study  of  the  Vegetation  of 

In  case  of  a  limited  but  severe  burn  in  the  midst  of  a  mixed 
forest,  provided  a  few  lodgepole  seed-trees  are  present,  the  fol- 
lowing generation  is  usually  predominated  by  the  lodgepole  pine. 
Provided  the  various  tree  seedlings  have  an  equal  start,  the  lodge- 
pole,  because  of  its  more  rapid  height-growth,  gains  an  ascend- 
ency over  its  neighbors.  Likewise,  by  its  habit  of  early  repro- 
duction (I  have  frequently  found  trees  only  seven  years  old  bear- 
ing cones)  it  furnishes  seeds  for  any  unoccupied  areas  or  for  the 
entire  area  if  seeds  of  other  trees  for  any  reason  fail  to  be  present. 
I  have  seen  a  few  such  areas  dominated  by  lodgepole  pine  but 
comparatively  they  are  not  abundant. 

But  because  of  its  early  maturity  and  its  inability  to  reproduce 
in  its  own  shade,  in  spite  of  the  advantage  gained  in  the  middle- 
aged  forest,  the  lodgepole  is  the  first  tree  to  drop  out  of  the 
mature  forest.  Unless  aided  by  another  fire  before  its  competitors 
reproduce,  it  assumes  a  less  and  less  important  role.  Indeed,  in 
most  of  the  forests  it  occurs  only  as  scattered  individuals,  al- 
though, as  previously  stated,  in  areas  cut  and  burned-over  thirty 
to  fifty  years  ago  the  lodgepole  pine  is  not  infrequently  an  im- 
portant tree. 

THE  HYDROSERE 

We  shall  now  take  up  the  development  of  the  hydrosere.  An 
outline  of  the  vegetational  units  of  this  sere  together  with  their 
relation  to  the  xerosere  may  be  found  on  page  19.  Because  of 
the  peculiar  topography  of  the  region,  combined  with  the  arid 
climate,  hydrophytic  and  meso-hydrophytic  communities  are  not 
widely  represented.  However,  along  the  streams  and  in  small 
ponds  and  lakes,  the  latter  occurring  especially  in  the  north- 
western part  of  the  region,  the  following  communities  are  found. 
The  three  well  marked  associes  of  the  water  sere  showing  strik- 
ing changes  of  habitat  and  life  form  as  well  as  definite  floristic 
differences,  are  those  dominated  by  submerged,  floating,  and 
swamp  plants  respectively,  in  their  successional  sequence.  The 
last  stage  is  succeeded  by  a  wet  meadow  community  which  is 
usually  followed  by  a  consociation  of  the  Agropyron-Festuca 
association  but  may  be  replaced  by  the  flood-plain  forest  associes. 

ioo 


Southeastern  Washington  and  Adjacent  Idaho.          101 

The  Chara-Potamogeton  Associes 

In  shallow  ponds  and  small  clear  streams  it  is  not  an  unusual 
sight  to  find  the  water  rather  completely  filled  with  various  sub- 
merged plants,  of  which  sometimes  Chara  and  sometimes  Pota- 
mogeton  pectinatus  or  P.  calif  ornicus  are  dominant.  Perhaps 
there  occurs  more  often  a  mictium  of  the  dominants  of  the  two 
consocies  respectively. 

In  addition  to  Vaucheria,  Stigeoclonium,  and  other  algae,  which 
are  frequently  very  abundant  in  such  situations,  Najas  flexilis, 
Zannichellia  palustris,  and  Batrachium  aquatile,  also  help  make 
up  the  tangle  of  submerged  plant  life. 

The  water  crowfoot  shows  great  plasticity  in  its  habitat  re- 
quirements, and  as  the  ponds  become  shallower  it  is  not  unusual 
to  find  it  dominating  considerable  areas  of  muddy  banks.  The 
aerial  leaves  with  their  well  developed  blades  appear  in  striking 
contrast  to  the  filiform  submerged  ones. 

-  The  role  of  these  submerged  plants  in  the  preparation  of  a 
suitable  substratum  for  later  stages  in  succession  is  frequently 
very  marked.  As  a  result  of  the  dense  aggregation  of  the  indi- 
viduals of  the  constituent  species  of  this  community,  bodies  of 
water  often  exhibit  a  pronounced  accumulation  of  debris  consist- 
ing for  the  most  part  of  the  remains  of  former  generations  of 
aquatic  plants  and  animals  but  mixed  ^ith  fine  soil  particles 
brought  in  by  the  action  of  wind  and  water,  the  whole  being 
effectively  held  in  position  by  the  expanding  tangle  of  living 
plants.  The  accumulation  of  humus  decreases  the  total  amount 
of  water  in  the  substratum  and  the  habitat  gradually  approaches 
a  little  nearer  the  mesophytic.  As  the  bottom  of  the  pond  is 
slowly  raised  by  the  accumulating  debris,  the  substratum  be- 
comes relatively  more  compact. 

A  continuation  of  these  processes  reacts  unfavorably  upon  the 
submerged  plants  and  they  thus  prepare  the  way  for  their  own 
elimination.  Not  only  is  the  reaction  of  initial  stages  of  succes- 
sion unfavorable  to  the  pioneer  plant  community  but  it  also  actually 
favors  invaders.  Plants  with  slender  stems  and  floating  leaves, 
such  as  Potamogeton  and  pond  lilies,  for  a -time  take  possession 

101 


IO2  A  Study  of  the  Vegetation  of 

of  the  shallowed  water,  while  through  the  agency  of  further 
humus  accumulation,  a  suitable  foothold  is  eventually  afforded 
for  the  development  of  cattails,  sedges,  rushes,  and  other  mem- 
bers of  the  marsh  community. 

About  the  margins  of  shallow  ponds  and  streams  and  often 
growing  in  shallow  water  are  to  be  found  Mimulus  langsdorfii, 
Veronica  spp.,  Radicula  spp.,  Ranunculus  alismaefolius,  or  Steiro- 
nema  ciliatum.  If  the  ponds  are  larger,  the  shallower  water  near 
the  margins  is  often  dominated  by  plants  of  the  following  com- 
munity : 

The  Nymphaea^Potamogeton  Associes 

Typically  this  associes  is  composed  of  plants  rooted  in  the  mud 
below  but  with  a  part  or  all  of  the  leaves  floating  on  the  water 
surface.  Their  general  position  in  the  sequence  of  succession  is 
following  that  of  the  submerged  forms,  whose  reaction  upon  the 
habitat,  as  previously  pointed  out,  is  to  shallow  the  water  and 
thus  make  it  less  fit  for  themselves  and  more  fit  for  the  anchored 
floating  forms. 

The  Marsilea  community  is  well  represented  in  certain  small 
ponds  but  is  most  conspicuous  in  the  rock  pockets  in  the  beds  of 
streams  during  the  dry  season.  The  ability  of  Marsilea  vestita 
to  float  on  the  surface  of  water  of  varying  depth  or  to  live  rooted 
in  the  mud  or  even  in  rather  dry  soil  fits  it  to  occupy  just  such  a 
changing  habitat.  However,  it  is  far  less  important  than  mem- 
bers of  the  following  consocies. 

The  Potamogeton  consocies  consists  of  various  species  of  Pota- 
mogeton  of  which  P.  americanus  often  is  dominant  (Fig.  29). 
Frequently  associated  with  it  are  the  submerged  P.  pectinatus 
and  P.  calif  ornicus.  In  late  summer  ponds  containing  the  latter 
species  are  sometimes  margined  for  considerable  distances  from 
the  shore  with  the  broadly  expanded  leaves  and  the  dense  spikes 
of  P.  americanus.  Associated  with  it  are  Polygonum  amphibium 
and  the  duckweeds,  Lemna  minor,  L.  trisulca,  and  locally,  Spiro- 
dela  polyrhiza. 

Other  ponds  and  especially  lagoons  along  the  upper  Palouse 
River  are  characterized  by  an  abundance  of  Nymphaea  poly- 

102 


Southeastern  Washington  and  Adjacent  Idaho.          103 

sepala,  whose  broad  leaves  and  pretty  yellow  flowers  almost  com- 
pletely cover  the  water  for  many  square  meters  (Fig.  30). 

Additional  floating-leaf  aquatics  are  occasionally  seen  in  mix- 
ture with  the  lily.  The  commonest  of  these  are  species  of 
Potam-ogcton  and  Alisnia  plantago-aquatica. 

Where  the  current  is  swift  enough  during  a  part  of  the  year 
to  keep  the  bottom  relatively  free  from  debris,  the  lily  community 
may  continue  for  years.  But  by  continued  humus  accumulation 
and  elevation  of  the  bottom,  the  habitat  becomes  invaded  more 
and  more  completely  by  plants  of  the  marsh  community  and 
finally  the  lilies  disappear  entirely. 

The  Scirpus-Typha  Associes 

Like  the  preceding,  the  associes  characterized  by  Scirpus  and 
Typha  is  found  covering  only  very  limited  areas  considering  the 
region  as  a  whole.  I  have  rarely  seen  the  two  dominants  grow- 
ing together,  and,  in  fact,  Typha  is  not  abundant.  However,  ob- 
servations on  Typha  in  its  limited  habitat  together  with  a  study 
of  its  relict  associates  in  shallow  water  show  rather  clearly  its 
place  in  the  succession. 

The  Scirpus  consocies  is  more  widely  represented.  The  domi- 
nant species  are  the  western  tule,  Scirpus  occidentalis,  and  Scir- 
pus microcarpus.  While  often  growing  in  rather  deep  water 
about  lake  margins  where  they  are  sometimes  associated  with 
relict  Nymphaea  and  Potamogeton,  they  likewise  occupy  boggy 
places,  which  in  late  summer  may  become  mere  mud  flats  (Fig. 
31).  Among  the  tall  stems  of  the  bulrushes  is  often  revealed  a 
distinct  layer  of  Alisma  plantago-aquatica,  Sagittaria  arifolia, 
and  Mentha  canadensis  borealis,  while  among  these  various 
species  of  creeping  buttercups  may  be  seen. 

Sometimes,  as  at  Tule  Lake,  a  slightly  higher  and  consequently 
drier  habitat  gives  a  fine  zonation  of  Eleocharis  palustris  and 
other  members  of  the  Eleocharis-Carex  community.  The  pres- 
ence of  the  latter  among  the  tule  in  the  drier  portions  of  its  area 
indicates  the  next  stage  of  development. 

103 


IO4  A  Study  of  the  Vegetation  of 

The  Eleocharis-Carex  Ass  odes 

This  plant  community  covers  areas  along  the  flood  plains  of 
smaller  streams  which  are  wet  during  the  rainy  season  but  often 
quite  dry  during  the  late  summer  months.  Likewise,  about  the 
borders  of  lakes  and  springs  it  occupies  situations  of  lower  water 
content  than  those  characterized  by  Scirpus  or  Typha. 

The  Eleocharis  consocies  is  dominated  by  E.  palustris.  It  some- 
times covers  considerable  areas  with  a  pure  growth  (Fig.  31). 
Its  rhizomes  form  extensive  mats  which  abound  at  the  edge  of 
ponds  as  well  as  in  the  shallow  water.  Associated  with  it  is  E. 
acicularis.  It  likewise  has  well  developed  and  extensive  root- 
stocks,  while  those  of  E.  acicularis  bella  are  very  short  so  that 
the  mats  assume  the  form  of  dense  round  tufts.  Because  of  its 
lesser  height-growth  the  latter  species  is  easily  distinguishable 
from  the  former. 

Frequently  occurring  in  mixture  with  Eleocharis  are  various 
sedges  and  rushes  of  the  following  community. 

The  Carex-Juncus  Mictium. — I  have  never  seen  in  this  region 
any  considerable  area  dominated  by  one  species  of  Car  ex  or 
Juncus.  However,  a  study  of  the  fragmentary  areas  charac- 
terized by  this  community  reveals  the  dominance  of  Car  ex  ne- 
braskensis  and  Juncus  balticus  locally.  More  often  the  follow- 
ing species  occur  in  a  puzzling  mictium : 

Car  ex  lanuginosa  Juncus  bufonius 

Car  ex  monile  pad  fie  a  Juncus  ensifolius 

Carex  nebraskensis  Juncus  suksdorfii 

Carex  pachystachya  Juncus  tenuis 
Juncus  balticus 

In  addition  to  relicts  of  the  preceding  communities,  associated 
with  the  above  species  are  to  be  found  numerous  other  plants  of 
which  the  most  important  are  Beckmannia  erucaeformis,  Radic- 
ula  curvisiliqua,  Alopecurus  calif ornicus,  Epilobiwn  adenocaulon, 
Carex  utriculata,  and  Mentha  canadensis  borealis.  The  last- 
named  plant  is  very  important  ecologically.  It  has  well  devel- 
oped and  extensive  rhizomes.  It  not  only  thrives  in  very  wet 

104 


Southeastern  Washington  and  Adjacent  Idaho.          105 

situations  but  likewise  occurs  abundantly  on  the  thin  soil  of  the 
stony  bottoms  of  intermittent  streams. 

The  Wet  Meadow  Associes 

The  wet  meadows  occupy  a  zone  lying  intermediate  in  succes- 
sion between  the  Eleocharis-Carex  associes  on  the  one  hand  and 
the  more  mesophytic  type  of  prairie  on  the  other.  As  would  be 
anticipated,  it  shows  all  stages  of  the  disappearance  of  relict 
members  of  the  Eleocharis-Carex  community  which  it  frequently 
borders,  as  well  as  the  invasion  of  the  more  mesophytic  prairie 
species. 

However,  the  community  as  a  whole  is  well  defined  and  is  es- 
pecially characterized  by  numerous  socies.  These  wet  meadows 
often  occupy  considerable  areas,  especially  near  the  mountains, 
and  under  cultivation  furnish  an  excellent  yield  of  timothy. 

Omitting  relicts  of  earlier  communities,  and  many  species 
found  typically  on  moist  hillsides,  the  following  list  gives  the 
principal  wet  meadow  species : 

Species  Forming  Distinct  Socies. — 

Deschampsia  caespitosa  Quamasia  quamash 

Hookera  hyacinthina  Ranunculus  platyphyllus 

Heracleum  lanatum  Veratrum  calif ornicum 

Iris  missouriensis  Wyethia  amplexicaulis 
Polygonum  bistortoides 

Other  Species. — 

Calochortus  nitidus  Hypericum  scouleri 

Car  ex  aperta  Lupinus  leucophyllus 

Castilleja  miniata  Mentha  canadensis  borealis 

Cicuta  occidentalis  Orthocarpus  tenuifolius 

Cogswellia  triternata  Poa  annua 

Delphinium  simplex  Poa  triflora 

Epilobium  adenocaulon  Polygonum  emersum 

Equisetum  spp.  Polygonum  polygaloides 

Galium  boreale  Potentilla  rectiformus 

Hordeum  nodosum  Prunella  vulgaris  lanceolata 

105 


io6  A  Study  of  the  Vegetation  of 

Rumex  mexicanus  Steironema  ciliatum 

Rumex  occidentalis  Trifolium  douglasii 

Senecio  serra  Zygadenus  venwwsus 
Sidalcea  oregana 

In  this  region  the  associes  is  represented  by  a  single  consocies, 
namely  that  dominated  by  Deschampsia  caespitosa.  This  char- 
acteristic grass  with  its  densely  tufted  perennial  stems,  which 
often  reach  a  height  of  over  3  feet,  often  occurs  in  nearly  pure 
growth.  In  favorable  situations,  the  clumps  may  reach  a  diame- 
ter of  9  inches. 

The  Quamasia  socies  is  well  marked  in  the  early  spring  when 
large  areas  in  the  wet  meadows  are  characterized  by  the  dark 
blue  flowers  of  Quamasia  quamash  (Fig.  32).  These  scapose 
plants,  reaching  a  height  of  2-2.5  f  eet> are  terminated  by  elongated 
racemose  clusters  of  as  many  as  30  large,  blue  flowers.  The  in- 
dividuals frequently  occur  as  abundantly  as  35-45  in  a  square 
meter.  The  edible  bulbs,  which  are  nearly  an  inch  in  diameter  and 
buried  only  4  inches  in  the  soil,  are  a  favorite  food  of  the  Indians. 

Heracleum  lanatum,  the  cow  parsnip,  is  very  abundant  in  wet 
meadows  along  streams  (Fig.  34).  It  not  only  reaches  far  above 
other  herbaceous  vegetation,  but  its  large  size  and  numerous, 
large,  white-flowered  umbels,  which  bloom  for  weeks,  make  this 
socies  a  very  conspicuous  one  for  the  major  part  of  the  growing 
season. 

Wet  meadows  in  early  spring  are  characterized  by  the  great 
abundance  of  Ranunculus  platy  phallus.  Its  great  numbers,  com- 
bined with  its  profuse  flowering  habit,  makes  this  socies  one  of 
the  most  important  of  the  vernal  period.  The  plant  has  rather  a 
bushy  habit.  Growing  about  2  feet  high,  it  often  spreads  at  the 
top  over  a  diameter  of  3  or  more  square  feet.  The  golden  yellow 
flowers  are  2.5  centimeters  in  diameter. 

Many  parts  of  the  wet  meadows  are  dominated  by  large  areas 
of  Iris  missouriensis.  The  growth  habit  of  this  cosmopolitan 
species  is  too  well  known  to  need  further  comment  here  (Fig.  33). 

The  black  sunflower,  Wyethia  amplexicaulis,  often  found  in 
rather  dry  prairies,  is  typically  at  home  in  the  wet  meadows. 

1 06 


Southeastern  Washington  and  Adjacent  Idaho.          107 

Often  the  gregarious  growths  almost  exclude  other  plants.  Its 
large,  dark-green,  shiny,  resinous  leaves,  more  than  a  foot  long 
and  as  many  as  20  on  a  single  individual,  are  no  less  characteris- 
tic than  its  numerous,  large  yellow  flowers.  A  single  plant  may 
occupy  an  area  of  more  than  2  square  feet  although  20-30  plants 
often  occur  in  a  single  quadrat.  It  possesses  a  strong  tap  root, 
5-9  inches  in  circumference,  which  may  penetrate  the  soil  to  a 
depth  of  over  6  feet. 

The  wet  meadow  is  gradually  replaced  upon  its  higher  lying 
borders  by  typical  prairie  species. 

It  should  be  mentioned  in  this  place  that  in  the  drier  regions 
large  areas  of  low-lying  ground  are  dominated  by  dense  growths 
of  rye-grasses,  especially  Elymus  condensatus.  In  low  ground 
such  as  dried  basins  of  shallow  ponds  and  where  the  soil  is  alka- 
line, socies  of  salt  grass,  Distichilis  spicata,  or  of  Spartina  gracilis 
are  to  be  found. 

The  Flood-plain  Forest  Associes 

The  flood-plains  along  the  streams,  because  of  the  seasonal  dis- 
tribution of  the  precipitation,  are  peculiarly  apt  to  be  subjected  to 
periodical  submergence.  Growing  in  these  rich,  well-watered, 
alluvial  soils  are  to  be  found  dense  thickets  of  various  trees  and 
shrubs  and  occasional  groves  of  poplars  and  aspens.  Since  the 
larger  streams  soon  cut  canyons  into  the  basalt,  the  flood-plains 
are  usually  not  extensive  and  the  zone  of  tree  growth  is  often 
limited,  especially  westward,  to  a  mere  fringe  along  the  bank  of 
the  streams  (Fig.  35).  Likewise  many  of  the  smaller  streams 
are  intermittent  and  along  these  thickets  of  woody  species  are 
few  or  entirely  absent.  A  close  relationship  exists  between  the 
protection  from,  wind,  afforded  flood-plain  areas  by  canyon  walls 
and  hills,  and  the  presence  or  absence  of  trees  and  shrubs. 

Although  these  flood-plain  'species  usually  occur  in  various 
mictia,  however,  two  communities  are  rather  well  defined — the 
Populus  consocies  and  the  Salix-Crataegus  mictium. 

The  Populus  Consocies. — Small  groves  of  poplars  consisting 
of  Populus  tremuloides,  or  more  rarely  of  Populus  trichocarpa 
are  frequent  along  the  flood  plains,  especially  in  the  less  arid  parts 

107 


io8  A  Study  of  the  Vegetation  of 

of  the  region.  These  usually  occur  in  situations  where  the  stream 
has  a  double  channel  or  where,  having  abandoned  one  channel,  it 
has  built  up  a  rich  alluvial  flat.  It  is  quite  clear  how  after  a 
spring  flood  the  wind-blown  seeds  of  the  poplars  find  excellent 
conditions  for  germination  in  such  situations  and  even  if  only  a 
few  become  established  the  extensive  underground  parts  of  Popu- 
lus  tremuloides  would  soon  increase  the  area  dominated  by  trees. 
In  this  manner  the  trembling  aspen  frequently  extends  its  terri- 
tory beyond  the  flood-plain  onto  the  moist,  sheltered  banks  of 
canyons.  I  have  observed  one  or  two  cases  in  the  deeper  canyons 
where  yellow  pines  had  established  themselves  among  the  aspens, 
and  seemed  to  be  replacing  them. 

The  Salix -Crataegus  Mictium. — Much  larger  areas  of  the  flood- 
plains  are  dominated  by  shrubs  or  trees  of  the  following  species ; 
these  may  occur  singly,  but  more  often  form  a  mictium. 

Alnus  tenuifolia  Salix  bebbiana 

Amelanchier  florida  Salix  cor  data 

Crataegus  brevispina  Salix  exigua 

Prunus  demissa  Salix  scouleriana 
Salix  argophylla 

In  addition  to  the  above  dominants  numerous  secondary  tree 
species  and  several  important  undershrubs  should  be  mentioned 
here.  The  following  are  the  most  important : 

Alnus  rhombifolia  Rosa  pisocarpa 

Amelanchier  cusickii  Ribes  aureum 

Betula  microphylla  Salix  bella 

Cornus  stolonifera  Salix  lasiandra  caudata 

Crataegus  columbiana  piperi  Salix  pyri folia 

Rosa  nutkana 

The  alder  sometimes  becomes  so  abundant  locally  as  to  consti- 
tute perhaps  half  of  the  flood-plain  woody  vegetation.  The 
chokecherry  is  never  so  abundant. 

Of  the  willows,  only  one,  Salix  lasiandra  caudata,  assumes  the 
proportions  of  a  tree.  As  might  be  anticipated,  the  willows  are 
usually  among  the  first  species  to  appear. 

108 


Southeastern  Washington  and  Adjacent  Idaho.         109 

Crataegus  brevispina  and  Amelanchier  florida  form  dense 
thickets,  sometimes  singly,  but  more  often  in  mictium.  Fre- 
quently these  copses  are  so  dense  as  to  exclude  all  other  vegeta- 
tion. In  the  month  of  May  when  these  trees  are  clothed  with 
their  profuse  white  blossoms  the  flood-plains  are  indeed  a  beauti- 
ful sight.  Even  in  winter  the  woodland  growth  along  the 
streams,  as  they  wind  their  way  among  the  treeless  hills,  lends 
pleasing  variety  to  the  monotonous  landscape. 

RUDERAL  VEGETATION 

There  are  a  number  of  plants  that  are  regularly  found  in  and 
about  waste  places.  To  this  number  may  be  added  others  that 
are  regular  members  of  certain  of  the  preceding  plant  communi- 
ties which  now  and  then  reveal  a  decidedly  ruderal  tendency. 
The  following  list  includes  the  commoner  plants  of  this  nature : 

RUDERAL  SPECIES 

Amaranthus  blitoides  Dipsacus  sylvestris 

Amaranthus  graecizans  Erigeron  canadensis 

Amaranthus  retroflexus  Er odium  cicutarium 

Amsinckia  intermedia  Geranium  pusillum 

Anthemis  cotula  Madia  glomerata 

Arctium  lappa  Marrubium  vulgare 

Artemisia  atomifera  Matricaria  matricarioides 

Artemisia  gnaphalodes  Polygonum  aviculare 

Bromus  brizaeformis  Salsola  kali  tenuifolia 

Chenopodium  botrys  Sanguisorba  annua 

Chenopodium  album  Sisymbrium  altissimum 

Cirsium  lanceolatum  Vaccaria  vaccaria 

Collinsia  tenella  Verbascum  thapsus 

Because  of  the  practice  of  alternating  a  crop  of  wheat  with 
summer  fallow  nearly  half  of  the  farmed  area  is  laid  bare  each 
year  for  the  invasion  of  ruderals.  Amaranthus  graecizans  and 
A.  retroflexus  are  the  dominant  weeds  of  these  fallow  fields. 
Unless  the  ground  is  frequently  tilled  these  grow  in  great  abun- 
dance, the  former  breaking  loose  near  the  surface  of  the  soil  in 

109 


iio  A  Study  of  the  Vegetation  of 

the  fall  of  the  year  and  tumbling  over  the  ground,  is  piled  by  the 
wind  into  great  heaps  on  the  leeward  slopes  of  the  hills. 

Westward,  in  the  drier  regions,  and  especially  in  the  scab-lands, 
Sisymbrium  altissimum,  locally  known  as  Jim  Hill  mustard,  from 
its  introduction  along  the  right  of  way  of  the  railroads,  is  pres- 
ent to  a  degree  almost  unbelievable.  Hundreds  of  acres  in  the 
scab-lands  are  literally  "  taken "  by  this  weed.  From  dwarfed 
specimens  a  few  centimeters  high  on  the  scab-rock,  it  ranges  to 
rank  growths 'in  the  moist  soil.  It  is  a  bad  weed  in  the  wheat 
fields  throughout  the  greater  part  of  the  region. 

The  tar  weed,  Amsinckia  intermedia,  is  likewise  a  troublesome 
weed  along  roadsides  and  especially  in  wheat  fields.  South  of 
Snake  River  it  is  very  abundant.  Its  dense  coat  of  long  bristly 
hairs  upon  drying  becomes  extremely  annoying  to  both  men  and 
horses. 

Westward  and  especially  in  the  slightly  alkali  regions  the  Rus- 
sian thistle,  Salsola  kali  tenui folia,  and  the  Australian  salt  bush, 
A  triplex  semibaccata,  are  often  abundant. 

Dipsacus  sylvestris,  introduced  a  number  of  years  ago,  has 
spread  very  rapidly  and  in  many  localities  assumes  the  role  of  a 
very  thrifty  and  very  obnoxious  weed. 

The  little  geranium,  Erodium  cicutarium,  is  an  introduced 
weed  which  has  become  very  common  in  gardens,  feed  lots,  and 
waste  places.  Often  associated  with  it  are  Sanguisorba  annua, 
Geranium  pusillum,  and  Verbascum  thapsus. 

Common  roadside  weeds  of  especial  abundance  are  Madia 
glomerata,  Marrubium  vulgare,  and  the  rattle  grass,  Bromus 
brizaeformis.  The  absence  of  most  roadside  weeds  so  common  in 
the  eastern  and  central  states  is  very  characteristic. 

About  the  numerous  grain-loading  stations  throughout  the 
region  many  ruderals  are  gaining  a  foothold.  Here  the  cars  are 
swept  out  and  the  seeds  of  various  plant  species  scattered. 
Among  other  weeds  thus  recently  introduced,  and  which  I  have 
seldom  seen  elsewhere,  may  be  mentioned  Ambrosia  trifida,  A. 
psilostachya,  Melilotus  alba,  M.  officinalis,  Cirsium  arvense,  Iva 
xanthifolia,  Datura  tatula,  and  Datura  stramonium.  The  prob- 
lem of  grain  warehouses  as  centers  of  weed  distribution  would 

no 


Southeastern  Washington  and  Adjacent  Idaho.          1 1 1 

form  in  itself  an  intensely  interesting  and  very  practical  field  of 
investigation. 

CONCLUSION 

In  the  foregoing  pages  it  has  been  shown  that  in  this  region 
lying  in  southeastern  Washington  and  adjacent  Idaho,  three  plant 
formations  occur.  In  the  western  part  of  the  region,  that  of  least 
elevation  and  consequently  of  lowest  precipitation,  the  desert 
scrub  formation  occurs.  As  the  altitude  becomes  greater  and  the 
climatic  conditions  more  favorable  eastward,  the  desert  scrub 
gives  way  to  the  grass  land  of  the  prairie-plains  formation.  In 
its  early  development  this  grass  land  is  of  a  very  open  bunch-grass 
type,  with  much  of  the  ground  being  either  destitute  of  vegeta- 
tion or  carpeted  with  interstitial  plants  only  in  early  spring.  As 
conditions  become  less  xerophytic  at  higher  altitudes  the  ground 
becomes  rather  completely  occupied  by  grasses,  some  of  which 
are  sod-formers,  and  by  non-grassy  herbaceous  vegetation  which 
shows  a  great  increase  both  in  the  number  of  species  and  in  the 
number  of  individuals  per  unit  area.  The  best  developed  prairies 
reveal  a  potential  shrub  community  which,  while  held  in  check 
usually  by  competition  with  prairie  plants,  develops  in  the  eastern 
edge  of  the  grass  lands  and  .especially  upon  the  non-basaltic  soils 
into  thickets  of  chaparral.  Under  cover  of  the  chaparral,  the 
yellow  pine,  a  pioneer  community  in  the  development  of  the 
Pacific  Coast  forests,  often  becomes  established.  The  pine  may 
be  replaced  by  Douglas  fir  and  tamarack,  and  these  in  turn  by 
mixed  communities  dominated  by  tamarack  and  white  fir,  or  by 
white  fir  and  cedar.  Finally,  in  the  most  mesophytic  areas  the 
cedar  community  reveals  the  climax  stage  in  the  development  of 
the  Pacific  Coast  forest  formation. 

It  has  been  shown  that  the  desert  scrub  formation  is  charac- 
terized by  soils  with  lower  water  content  and  higher  temperature, 
and  with  higher  evaporating  power  of  the  air  than  any  of  the 
other  plant  communities.  Likewise,  there  has  also  been  found  to 
exist  in  the  several  plant  communities  of  the  xerosere,  from  the 
bunch-grass  community  of  the  prairies  to  the  climax  cedar  com- 
munity of  the  forest,  a  direct  relation  between  the  water  content 

1 1 1 


112  A  Study  of  the  Vegetation  of 

of  the  soil,  the  temperature  of  the  soil  and  the  evaporating  power 
of  the  air,  and  progressive  stages  in  succession.  The  water  con- 
tent of  the  soil  has  been  found  to  vary  directly  with  the  stages  of 
the  sere  from  a  minimum  in  the  bunch-grass  stage  to  a  maximum 
in  the  cedar  community.  Conversely,  the  soil  temperature  and 
the  evaporating  power  of  the  air  have  been  shown  to  decrease 
directly  in  proportion  to  the  advancement  of  the  stage  of  develop- 
ment of  the  sere. 

In  the  forest  communities  the  light  values  decrease  progress- 
ively as  the  climax  community  is  approached. 

In  addition  to  the  xerosere,  beginning  with  lichens  and  mosses 
on  the  bare  rocks  of  basalt,  granite,  or  quartzite  and  ending  ulti- 
mately in  the  climax  forest  community,  we  have  also  traced  the 
stages  of  the  subsere  in  the  reestablishment  of  cut-over  or  burned- 
over  forested  areas.  We  have  seen  how  these  more  or  less  de- 
nuded areas  may  finally  come  to  support  the  same  type  of  vegeta- 
tion that  characterized  them  before  the  disturbance  of  their 
normal  development. 

Lastly,  we  have  considered  the  hydrosere.  The  communities  of 
this  sere,  although  occupying  a  relatively  small  area  geograph- 
ically, show  distinct  stages  from  the  submerged,  floating  and 
swamp  communities  to  that  of  the  wet  meadow.  The  latter  is 
usually  replaced  by  a  xerophytic  grass  land  community,  or  infre- 
quently by  a  deciduous  flood-plain  forest. 

In  concluding  this  report  on  the  study  of  the  vegetation  of 
southeastern  Washington  and  adjacent  Idaho,  the  writer  wishes 
to  state  that  perhaps  no  one  feels  more  keenly  than  he  the  neces- 
sarily preliminary  nature  of  the  work  accomplished. 

The  Snake  River  Canyon  alone,  with  its  peculiarly  dry,  mild 
climate  stands  in  marked  contrast  to  the  colder,  more  humid  area 
above,  and  forms  a  rich  field  for  detailed  ecological  investigation. 
Not  infrequently  has  the  writer  spent  days  in  late  February  or 
early  March  among  the  abundant  prevernal  flora  of  the  canyon, 
while  weeks  later  most  of  the  same  species  came  into  blossom  on 
the  plateau  above,  while  yet  another  period  elapsed  before  the 
awakening  of  the  same  species  on  butte  and  mountain  prairies. 

During  the  progress  of  this  study  a  number  of  plant  species 

I  12 


Southeastern  Washington  and  Adjacent  Idaho.          113 

not  reported  for  the  region  were  encountered.  Among  these  the 
occurrence  of  the  devil's  club,  Echinopanax  horridum,  along  cer- 
tain streams  in  Thatuna  Hills,  is  especially  interesting.  Many 
of  the  species  new  to  the  region  are  ruderals.  Other  plants  like 
Crataegus  columbiana  piperi,  heretofore  known  to  occur  only  in 
Washington,  were  also  repeatedly  found  in  Idaho. 

It  is  hoped  that  the  results  of  the  present  research  may  form 
a  basis  for  further  investigation  of  the  ecological  problems  of 
this  and  adjoining  regions. 

LITERATURE  CITED 

1.  Calkins,  F.  C.     Geology  and  Water  Resources  of  a  Portion  of  East- 

central  Washington.     Water-supply  paper  U.  S.  Geological  Survey 
No.  118,  1905. 

2.  Clements,  F.  E.     Plant  Succession.     Carnegie  Inst.  Wash.   Publ.,  242, 

1916. 

3.  Frye,  Theodore  C.,  and  Rigg,  George  B.     Northwest  Flora,  1912. 

4.  Fuller,  George  Damon.     Evaporation  and  Plant  Succession.     Bot.  Gaz., 

52:  193-208,  1911. 

5.  Fuller,  George   Damon.     Evaporation   and   Soil   Moisture   in   Relation 

to  Succession  of  Plant  Associations.     Bot.  Gaz.,  58:  193-234,  1914. 

6.  Humphrey,  Harry  B.,  and  Weaver,  John  Ernst.     Natural  Reforesta- 

tion in  the  Mountains  of  Northern  Idaho.     Plant  World,  18:  31-48, 


7.  Hoffman,    Julius    V.     Natural    Reproduction    of    Coniferous    Forests. 

Univ.  Minn.  Studies  Biol.  Sci.,  I. 

8.  Landes,  Henry.     Underground  Waters  of  Washington.     Water-supply 

and  Irrigation  Paper,  No.  in,  1905. 

9.  Piper,  Charles  V.     Flora  of  the  State  of  Washington.     Contributions 

from  the  U.  S.  National  Herbarium,  n:  1906. 
10.  Piper,  Charles  V.,  and  Beattie,  R.  Kent.     Flora  of  the  Palouse  Region, 

1901. 
n.  Piper,  Charles  V.,  and  Beattie,  R.  Kent.     Flora  of  Southeastern  Wash- 

ington and  Adjacent  Idaho,  1914. 

12.  Russell,    I.    C.     Principal   Features   of    the    Geology   of    Southeastern 

Washington.     Mining,  3  :  163-165,  1897. 

13.  Russell,    I.    C.     Reconnaissance    in    Southeastern    Washington.     U.    S. 

Geol.  Surv.,  Water-supply  and  Irrigation  Paper  No.  4,  1897. 

14.  Russell,   I.    C.     Geology   and   Water,  Resources   of    the    Snake   River 

Plains  of  Idaho.     Bull.  U.  S.  Geol.  Surv.,  No.  199,  1902. 

15.  Turesson,    G.     Slope   Exposure   as   a   Factor   in    the    Distribution    of. 


114  A  Study  of  the  Vegetation  of 

Pseudotsuga    taxifolia    in    Eastern    Washington.     Bull.    Torr.    Bot. 
Club,  41  :  337-345,  IQH- 

16.  Weaver,   John   Ernst.     Evaporation   and    Plant   Succession   in   South- 

eastern Washington  and  Adjacent  Idaho.     Plant  World,   17:  273- 
294,  1914. 

17.  Weaver,  John  Ernst.     A  Study  of  the  Root-systems  of  Prairie  Plants 

of  Southeastern  Washington.     Plant  World,  18:  227-248  and  273- 
292,  1915. 

18.  Whitford,  H.  N.     The  Forests  of  the  Flathead  Valley,  Montana.     Bot. 

Gaz.,  39:  99-122,  194-218,  276-296,  1905. 


114 


FIG.  16.  Typical  view  in  the  sagebrush  community.  The  chief  plant  is 
the  scab-land  sage,  Artemisia  rigida.  The  hills  in  the  background  are 
covered  with  bunch-grass. 


FIG.  17.  A  glimpse  of  the  lichen-moss  community.  The  black  mats  are 
Grimmiamontana.  Surrounding  the  base  of  the  rocks  a'nd  extending  along 
the  deeper  crevices  are  patches  of  Tortula  into  which  the  June  grass  is 
invading. 


i8.     June  grass  and  knotgrass  on  thin  rocky  soil.     Note  the  bunch- 
grass  occupying  the  deeper  soil  in  the  background. 


FIG.  19.     A  typical  bunch-grass  community.     Much  of  the  soil  surface  is 

unoccupied. 


FIG.  20.    A  hillside  in  Garfield  County  clothed  with  plants  of  the  Agropyron 
consociation.     Typical  representation  of  the  drier  type  of  prairie. 


FIG.  21.     Festuca  consociation  in  eastern  Whitman  County;  representative 
of  the  less  xerophytic  type  of  prairie. 


FIG.  22.  Minor  quadrat  in  the  Festuca  consociation.  The  conspicuous 
plants  are  Balsamorhiza  sagittata,  Hieracium  scouleri,  and  Festuca  ovina 
ingrata.. 


FIG.  23.  Yellow  pines  invading  a  protected  north  slope  under  cover  of 
the  ninebark,  Opulaster  pauciflorus.  The  exposed  south  slope  is  covered 
with  prairie,  tongues  of  which  extend  down  the  dry  ridges  shown  in  the 
picture. 


Southeastern  Washington  and  Adjacent  Idaho.          119 


119 


FIG.  25.     Douglas  fir  and  yellow  pine  on  an  exposed  rocky  slope  in  the 

mountains. 


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FIG.  26.     A  mixed  forest  of  Douglas  fir,  tamarack,  and  white  fir. 


Southeastern  Washington  and  Adjacent  Idaho.          121 


FIG.  27.     A  glimpse  into  a  primeval  forest  of  Larix,  Abies,  and  Thuja. 


121 


FIG.  28.     Climax  Thuja  consociation.     In  such  situations  the  light  is  too 
low  to  permit  the  growth  of  tree  seedlings  other  than  the  cedar. 


FIG.   29.     Potamogeton   consocies    in    Silver   Lake.     The   chief    species   is 
Potamogeton  americanus.     Willows  fringe  the  margin  of  the  lake. 


FIG.  30.     A  consocies  of  Nymphaea  in  a  lagoon  of  the  Palouse  River. 


FIG.  31.  View  near  Rock  Lake  showing  zonation  of  Eleocharis  palus- 
tris  (foreground)  and  Scirpus  microcarpus.  In  the  background  are  flood- 
plain  trees  of  willow,  hawthorne,  and  Amelanchier. 


FIG.  32.     A  wet  meadow  socies  of  Quamasia  quamash. 


FIG.  33.     A  socies  of  Iris  missouriensis. 


Southeastern  Washington  and  Adjacent  Idaho, 


125 


FIG.  34.    Heracleum  lanatum  and  Crataegus  brevispina  in  a  wet  meadow. 


FIG.  35.  A  view  of  the  flood-plain  trees  along  Rock  Creek  in  western 
Whitman  County.  The  chief  trees  are  Betula  microphylla,  Crataegus  brevi- 
spina, and  species  of  Salix. 


FIG.  36.  A  view  of  Kamiak  Mountain  looking  northward  from  Smoot 
Hill.  Note  the  fringe  of  pines  near  the  summit  of  the  exposed  south 
slope. 


FIG.   37.    .The  north   slope   of   Kamiak   Mountain.     It  -is   covered   with   a 
second-growth  forest  of  Douglas  fir  and  tamarack. 


FIG.  38.     A  bit  of  skyline  at  Pullman,  Washington,  showing  the  rounded, 
flowing  outlines  of  the  dune-like  topography. 


FIG.  39.  A  view  in  the  scab-lands  in  eastern  Adams  County.  A  dis- 
tance of  a  few  feet  may  show  a  change  of  vegetation  from  the  lichens  and 
mosses  on  the  rocks  to  the  June  grass — knot-grass  or  sagebrush  com- 
munities. Likewise,  the  bunch-grass  and  balsam-root  of  the  drier  soil 
gives  way  to  more  mesophytic  species  in  the  depressions. 


FIG.  40.     A  family  of  knot-grass  invading  a  newly  formed  talus  slope. 


FIG.  41.     Base  station   in  the  Festuca  consociation  near  Pullman,  Wash. 


FIG.  42.     A  single  plant  of  Balsam  or hisa  sagittata. 


Southeastern  Washington  and  Adjacent  Idaho. 


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A  Study  of  the  Vegetation  of 


FIG.  44.  A  five-year-old  burn  on  a  dry  slope  in  Thatuna  Hills.  Under 
the  cover  of  the  fireweed  numerous  seedlings  of  yellow  pine,  Douglas  fir, 
and  tamarack  are  to  be  found. 


Southeastern  Washington  and  Adjacent  Idaho.          131 


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FIG.  46.     A   sharp   ecotone  between   prairie  and   forest  on   a  wind-swept 
slope  in  Tekoa  Mountains. 


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FIG,  47.  The  bunch-grass,  Agropyron  spicatum.  Diagrammatic  cross- 
section  and  detailed  segment  of  a  leaf  showing  its  xerophytic  anatomical 
structures. 


FIG.  48.     Bunches  of  Festuca  ovina  ingrata.     The  cross-section  of  one  of 
the  setaceous  leaves  shows  that  it  is  well  adapted  to  endure  drought 


PB  00053  69-vS3 
16 


STORED  AT  NRLF 


QK941  .W2W4  Sci 


3  2106  00255   1270 


